% \iffalse meta-comment
%
% Copyright (C) 2016-2018 by Richard Grewe <r-g+tex@posteo.net>
% -------------------------------------------------------
% 
% This file may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either version 1.2
% of this license or (at your option) any later version.
% The latest version of this license is in:
%
%    http://www.latex-project.org/lppl.txt
%
% and version 1.2 or later is part of all distributions of LaTeX 
% version 1999/12/01 or later.
%
% \fi
%
% \iffalse
%<*driver>
\ProvidesFile{multilang.dtx}
%</driver>
%<package>\NeedsTeXFormat{LaTeX2e}[1999/12/01]
%<pkgtags>\NeedsTeXFormat{LaTeX2e}[1999/12/01]
%<pkgsect>\NeedsTeXFormat{LaTeX2e}[1999/12/01]
%<package>\ProvidesPackage{multilang}
%<*package>
    [2018/11/02 v0.9b Tools for maintaining documents in multiple languages]
%</package>
%<pkgtags>\ProvidesPackage{multilang-tags}[2018/11/02 v0.9b Filtering of multilingual macros by tags]
%<pkgsect>\ProvidesPackage{multilang-sect}[2018/11/02 v0.9b Multilingual sectioning environments]
%
%<*driver>
\documentclass{ltxdoc}
\usepackage[columns=2]{idxlayout}
\usepackage{xcolor}
\usepackage{xspace}
\usepackage[inline]{enumitem}
\usepackage{showexpl}
\lstset{gobble=2,frame=trbl,backgroundcolor=\color{black!5!white},width=0.475\textwidth}
\lstset{basicstyle=\footnotesize\fontfamily{pcr}\selectfont}
\lstset{explpreset={columns=fixed,numbers=none,language={}}}
\lstset{preset={\small\sffamily},overhang=2cm,pos=r,varwidth=false}
\usepackage{pbox}
\newcommand\NiceDescribeStuff[2]{% #1=margin text, #2=body text
  \medskip\par\noindent\leavevmode%
  \marginpar{\hfill\pbox[t]{2\marginparwidth}{\ttfamily #1}%
    \hspace*{-\marginparsep}}%
  \ifstrempty{#2}{}{#2\smallskip\\}}
\newcommand\NiceDescribeEnv[3][]{% #1=index list, #2=envname, #3=parameters
  \NiceDescribeStuff{%
    \textcolor{gray}{\cs{begin}}\string{#2\string}\\
    \textcolor{gray}{\cs{end}}\string{#2\string}}{#3}%
  \ifstrempty{#1}
    {\SpecialEnvIndex{#1}}%
    {\forcsvlist{\SpecialEnvIndex}{#1}}%
  \ignorespaces}
\newcommand\NiceDescribeMacro[2]{% #1=macro, #2=parameters
  \NiceDescribeStuff{\hbox to 0pt{\hss\string#1}}{#2}%
  \SpecialUsageIndex{#1}\ignorespaces}
\newcommand\NiceDescribeConstant[1]{% #1=constant
  \NiceDescribeStuff{\hbox to 0pt{\hss #1\quad}}{}\ignorespaces}
\makeatletter
\newcommand\SaveSecs{%
  \@for\SC:=section,subsection,subsubsection\do{%
    \csedef{SC@\SC}{\the\value{\SC}}%
    \setcounter{\SC}{0}}}
\newcommand\RestoreSecs{%
  \@for\SC:=section,subsection,subsubsection\do{%
    \setcounter{\SC}{\csuse{SC@\SC}}}}
\makeatother
\newcommand\ThisPackage{\textsf{multilang}\xspace}
\usepackage{hypdoc}
\usepackage[capitalise,nameinlink]{cleveref}
% the following packages are for the examples
\usepackage[german,english]{babel}
\usepackage[languages={english,german}]{multilang}
\usepackage[autostyle=true]{csquotes}
\usepackage[useregional]{datetime2}
\usepackage{sectionbox}
\usepackage{translations}
\usepackage{multilang-tags}
\usepackage{multilang-sect}
% end of examples packages
\EnableCrossrefs
\CodelineIndex
\RecordChanges
\begin{document}
  \DocInput{multilang.dtx}
  \PrintChanges
  \PrintIndex
\end{document}
%</driver>
% \fi
%
% \CheckSum{0}
%
% \CharacterTable
%  {Upper-case    \A\B\C\D\E\F\G\H\I\J\K\L\M\N\O\P\Q\R\S\T\U\V\W\X\Y\Z
%   Lower-case    \a\b\c\d\e\f\g\h\i\j\k\l\m\n\o\p\q\r\s\t\u\v\w\x\y\z
%   Digits        \0\1\2\3\4\5\6\7\8\9
%   Exclamation   \!     Double quote  \"     Hash (number) \#
%   Dollar        \$     Percent       \%     Ampersand     \&
%   Acute accent  \'     Left paren    \(     Right paren   \)
%   Asterisk      \*     Plus          \+     Comma         \,
%   Minus         \-     Point         \.     Solidus       \/
%   Colon         \:     Semicolon     \;     Less than     \<
%   Equals        \=     Greater than  \>     Question mark \?
%   Commercial at \@     Left bracket  \[     Backslash     \\
%   Right bracket \]     Circumflex    \^     Underscore    \_
%   Grave accent  \`     Left brace    \{     Vertical bar  \|
%   Right brace   \}     Tilde         \~}
%
% \changes{v0.9}{2017/08/30}{Initial version}
% \changes{v0.9b}{2018/11/02}{Package author's name change}
%
% \GetFileInfo{multilang.dtx}
%
% \DoNotIndex{\newcommand,\newenvironment,\def,\gdef,\edef}
%
%
% \title{The \ThisPackage package\thanks{This document
%   corresponds to \ThisPackage~\fileversion, dated \filedate.
%   The package is available online at
%   \url{http://www.ctan.org/pkg/multilang} and
%   \url{https://github.com/Ri-Ga/multilang}.}}
% \author{Richard Grewe \\ \texttt{r-g+tex@posteo.net}}
%
% \maketitle
%
% \begin{abstract}
%   Maintaining a \LaTeX{} document with translations for multiple languages
%   can be cumbersome and error-prone.
%   The \ThisPackage package provides a set of macros for defining macros and
%   environments as wrappers around existing macros and environments.
%   These wrappers allow one to clearly specify multiple translations for the
%   arguments to the wrapped macros and environments while only the
%   translation of the document's language is actually shown.
%   Choosing a translation then is as simple as choosing the document's
%   language via \textsf{babel} or \textsf{polyglossia}.
% \end{abstract}
%
% \section{Introduction}
% \label{sec:Introduction}
%
% The main goal of the \ThisPackage package is to facilitate the
% definition of macros and environments with which documents can be
% provisioned in multiple languages.
% To be more concrete, \ThisPackage facilitates
% \begin{enumerate}
% \item the specification of content translations:
%
%   \begin{itemize}[noitemsep]
%   \item Arguments to macros are specified by their name such that multiple
%     translations do not clutter up the \LaTeX{} code that easily.
%   \item If you forget to specify a mandatory argument in a language,
%     \ThisPackage shows an error when you compile for that language.
%   \end{itemize}
%
% \item the maintenance of translations:\smallskip
%
%   Translations of content that is passed as an argument to a macro can be kept
%   closely together such that you can keep track of which units belong together
%   and can keep consistency among translations across content changes.
%
% \item the selection of a document language:\smallskip
%
%   You simply specify the language with \textsf{babel} or \textsf{polyglossia}
%   and \ThisPackage selects the translation you provided for the language.
% \end{enumerate}
%
% The motivating example that lead to the development of this package are CVs
% (curricula vitae). Suppose you want to maintain a CV document that contains
% the union of all your relevant personal data, education, achievements, etc.
% You update the CV from time to time with new achievements. Since you want to
% prepare for the possibility that you might apply nationally as well as
% internationally, you maintain the CV document in multiple languages (e.g.,
% your mother language and English).
% When you use the CV in a concrete job application, you
% \begin{enumerate*}[label=(\arabic*)]
% \item filter out all details that are irrelevant for the position that you
%   apply for
%   and
% \item select a suitable language for the employer.
% \end{enumerate*}
%
% This package provides a set of basic macros for the definition of
% multilingual macros and multilingual environments. The following example
% illustrates such a macro and how it could be used.
% \SaveSecs
%
% \begin{LTXexample}[preset={\newcommand\Sec[1]{\section{Foobar}}}]
% % ...
% \usepackage[german,english]{babel}
% \usepackage[languages={english,german}]
%            {multilang}
% % ...
% \begin{document}
% \Sec{
%   title/english={Foobar},
%   title/german ={Dingsda}
% }
% ...
% \end{document}
% \end{LTXexample}
% \RestoreSecs
% \Cref{sec:Usage} describes how a macro such as |\Sec| in the above
% example can be defined with \ThisPackage. The \lcnamecref{sec:Usage} also
% describes how analogous environments can be defined.
% \Cref{sec:Types} describes extensible argument types.
% \Cref{sec:Extensions} describes two extension packages,
% \textsf{multilang-sect} and \textsf{multilang-tags} for multilingual
% sectioning and, respectively, for filtering multilingual macros and
% environments.
%
%
% \section{Usage}
% \label{sec:Usage}
%
% \subsection{Package Options}
%
% \NiceDescribeConstant{languages}
% The \ThisPackage package has a single option: |languages|. This option
% expects a comma-separated list of language names. The ordering of the list
% does not make a difference. Through this option, one sets the languages for
% which translations can be provided. By default, the list is empty such that
% no translations can be specified.
% The example in \cref{sec:Introduction} demonstrates how this option can be
% used.
%
%
% \subsection{Multilingual Macros}
% \label{sec:Usage-Macros}
%
% \NiceDescribeMacro{\NewMultilangCmd}{\marg{command}\marg{options}}
% A multilingual macro can be defined via the |\NewMultilangCmd| macro.
% The macro defines \meta{command} as a macro that accepts a single argument.
% That is, the signature of \meta{command} is \meta{command}\marg{kvarg}. The
% argument, \meta{kvarg}, is a comma-separated key-value list.
% The \meta{options} argument takes the form of a comma-separated key-value
% list and specifies what \meta{command} does, including how \meta{kvarg} is
% interpreted. The following keys are defined for \meta{options}:
% \begin{description}[noitemsep]
% \item[|command|:]
%   This key is to be used in the form ``|command=|\meta{c}'', where \meta{c}
%   is an already existing command.
%   The key specifies that \meta{command} is defined to invoke \meta{c} with
%   some arguments.
%   Example: see \cref{sec:Usage-margs}.
% \item[|margs|:]
%   This key is to be used in the form ``|margs={|\meta{csvlist}|}|'', where
%   \meta{csvlist} is a comma-separated list of names.
%   The key specifies names for the mandatory arguments of \meta{c}, in the
%   order specified.
%   If \meta{c} is a macro that takes $n$ mandatory arguments, then
%   \meta{csvlist} should be a list of $n$ names. If \meta{arg-i} is the
%   $i$-th entry in \meta{csvlist}, then the $i$-th mandatory
%   argument to \meta{c} can be specified as \meta{v} in the invocation of
%   \meta{command} as follows:
%      ``\meta{command}|{...,|\meta{arg-i}|=|\meta{v}|,...}|''.
%   Example: see \cref{sec:Usage-margs}.
% \item[|oargs|:]
%   This key is to be used in the form ``|oargs={|\meta{csvlist}|}|'', where
%   \meta{csvlist} is a comma-separated list of names.
%   This key is analogous to |margs|, but for optional arguments to \meta{c}.
%   Example: see \cref{sec:Usage-oargs}.
% \item[|starred|:]
%   This key is to be used simply as
%     ``|starred=|\meta{bool}'', where \meta{bool} must be |true| or |false|,
%   or just as ``|starred|'', which is equivalent to ``|starred=true|''.
%   If \meta{bool} is |true|, then ``\meta{command}|*{...}|'' can be used to
%   invoke ``\meta{c}|*...|''.
%   Example: see \cref{sec:Usage-starred}.
% \item[|disablable|:]
%   This key is to be used simply as
%     ``|disablable=|\meta{bool}'', where \meta{bool} must be |true| or |false|,
%   or just as ``|disablable|'', which is equivalent to ``|disablable=true|''.
%   If \meta{bool} is |true|, then the invocation of \meta{c} in
%   \meta{command} can be suppressed via
%   ``\meta{command}|{...,disabled,...}|''.
%   Example: see \cref{sec:Usage-disablable}.
% \item[|defaults|:]
%   This key is to be used as
%   ``|defaults={...,|\meta{arg}|=|\meta{value}|,...}|''.
%   Each key \meta{arg} should be the name of an optional or mandatory
%   argument and \meta{value} should be the intended default value for this
%   argument.
%   Example: see \cref{sec:Usage-defaults}.
% \item[|alias/...|:]
%   This key is to be used as ``|alias/|\meta{name}|={|\meta{arglist}|}|'',
%   where \meta{name} specifies the name of the alias and \meta{arglist} is a
%   possibly empty comma-separated list of argument names (optional or
%   mandatory arguments allowed).
%   Example: see \cref{sec:Usage-alias}.
% \end{description}
% The remainder of \cref{sec:Usage-Macros} provides examples based on the
% |\section| macro.
%
%
% \subsubsection{Basic Usage}
% \label{sec:Usage-margs}
% The following example shows how the |\Section| macro used in the example of
% \cref{sec:Introduction} can be defined. We leave out the \textsf{babel} code
% in this \lcnamecref{sec:Usage} for more concise example code.
%
% \SaveSecs
% \begin{LTXexample}[morekeywords={NewMultilangCmd,command,margs}]
% \NewMultilangCmd{\Sec}{
%   command=\section, margs=title}
% \Sec{
%   title/english={Foobar},
%   title/german ={Dingsda}
% }
% \end{LTXexample}
% \RestoreSecs
%
%
% \paragraph{Language-independent arguments.}
% Sometimes, arguments to macros need no translation. For instance, if an
% argument is a technical term or a name, it can remain in the original
% language. To avoid redundancy, in such instances the language part of a
% mandatory or optional argument can be omitted to specify the argument for
% all languages.
%
% \SaveSecs
% \begin{LTXexample}[preset={\NewMultilangCmd{\Sec}{margs=title,oargs=short,command=\section}}]
% \Sec{title=multilang}
% \end{LTXexample}
% \RestoreSecs
%
%
% \paragraph{Forced foreign-language arguments.}
% \label{sec:Usage-forced-language}
% A particular instance of a language-independent argument is the case in which
% the argument shall explicitly be typeset in a particular language. For
% instance, the argument might use macros that internally determine the
% display based on the selected language. The following example shows the case
% of forcing German display of the |\enquote| macro.
% 
% \SaveSecs
% \begin{LTXexample}[preset={\NewMultilangCmd{\Sec}{margs=title,oargs=short,command=\section}}]
% \usepackage[autostyle=true]{csquotes}
% %...
% \Sec{title/german!=\enquote{multilang}}
% \end{LTXexample}
% \RestoreSecs
%
%
% \subsubsection{Optional Arguments}
% \label{sec:Usage-oargs}
% Macros like |\section| don't just have a mandatory argument (the section
% title) but also an optional argument (a short title for the table of
% contents). We can make this optional argument accessible via the |oargs|
% option as follows.
% The displayed result does not show any difference as we don't have the table
% of contents here.
%
% \SaveSecs
% \begin{LTXexample}[morekeywords={oargs}]
% \NewMultilangCmd{\Sec}{
%   command=\section, margs=title, oargs=short}
% \Sec{
%   title/english={Foobar},
%   title/german ={Dingsda},
%   short/english={F},
%   short/german ={D},
% }
% \end{LTXexample}
% \RestoreSecs
%
%
% \subsubsection{Starred Macros}
% \label{sec:Usage-starred}
% Some macros can be altered in their behavior with a star (``|*|'') after the
% macro. The |\section| command is an example of such a macro: |\section*|
% suppresses the display of the section number. The star can be transferred to
% the command defined via |\NewMultilangCmd| as the following example
% illustrates.  Note the exclamation mark after ``|german|''.
%
% \SaveSecs
% \begin{LTXexample}[morekeywords={starred}]
% \NewMultilangCmd{\Sec}{starred,
%   command=\section, margs=title, oargs=short}
% \Sec{title=Foo}
% \Sec*{title=Bar}
% \end{LTXexample}
% \RestoreSecs
%
%
% \subsubsection{Disabling Display}
% \label{sec:Usage-disablable}
% When a macro is defined with the |disablable| option, it can be passed the
% |disabled| argument which disables the display of the macro. One might
% consider this a nicer way to disable content than commenting out the macro.
% 
% \SaveSecs
% \begin{LTXexample}[morekeywords={disablable}]
% \NewMultilangCmd{\Sec}{disablable,
%   command=\section, margs=title, oargs=short}
% \Sec{title=Foo}
% \Sec{title=Bar,disabled}
% \end{LTXexample}
% \RestoreSecs
%
%
% \subsubsection{Default Arguments}
% \label{sec:Usage-defaults}
% When a mandatory or optional argument shall by default assume a particular
% value if no value is specified for the argument in the argument to
% \meta{command}, this can be specified via the |defaults| key as the
% following example demonstrates.
%
% \SaveSecs
% \begin{LTXexample}[morekeywords={defaults}]
% \NewMultilangCmd{\Sec}{
%   command=\section, margs=title,
%   defaults={title={???}}}
% \Sec{}
% \end{LTXexample}
% \RestoreSecs
% Defaults can be particularly useful for mandatory arguments of commands
% that take multiple arguments and that can often be left empty.
% Essentially, argument defaults turn mandatory arguments of
% macros to optional arguments.
%
%
% \subsubsection{Argument Aliases}
% \label{sec:Usage-alias}
% Aliases allow one to specify argument names of three different kinds:
% \begin{description}[nosep]
% \item[direct aliases:]
%   A direct alias declares an argument name that can then be used as a
%   substitute for some mandatory or optional argument.
%   The |heading| argument in the following example shows how direct aliases
%   can be declared.
% \item[combiner aliases:]
%   A combiner alias declares an argument name that acts as a substitute for a
%   sequence of mandatory or optional arguments.
%   Such aliases particularly help maintaining concise \LaTeX{} source code
%   when argument values are rather short, as |both| in the following example
%   shows.
% \item[comment aliases:]
%   A comment alias declares an argument name that represents no mandatory or
%   optional argument. That is, a value specified for a comment alias is not
%   used as an argument to the |command| and can, hence, be used for capturing
%   comments or values for future use.
% \end{description}
%
% \SaveSecs
% \begin{LTXexample}[morekeywords={alias}]
% \NewMultilangCmd{\Sec}{
%   command=\section, margs=title, oargs=short,
%   alias/heading=title,
%   alias/both={title,short},
%   alias/remark}
% \Sec{
%   both/english={Foobar}{Foo},
%   both/german ={Dingsda}{Dings}}
% \Sec{
%   heading=Baz,
%   remark={select heading+translate}}
% \end{LTXexample}
% \RestoreSecs
%
%
% \subsection{Multilingual Environments}
%
% \NiceDescribeMacro{\NewMultilangEnv}{\marg{environment}\marg{options}}
% The usage of the |\NewMultilangEnv| macro is analogous to the usage of
% the macro |\NewMultilangCmd|, except for the following differences:
% \begin{itemize}[noitemsep]
% \item The first argument, \meta{environment}, expects the name of an
%   environment that shall be defined.
% \item In the \meta{options}, the |environment| key substitutes the |command|
%   key and expects an environment name.
% \item The |starred| key is not available. Following standard \LaTeX{}
%   practices, if you want to define a starred environment, simply use the
%   starred name for \meta{environment}.
% \end{itemize}
% Due to the similarity to |\NewMultilangCmd|, we don't provide separate
% examples for all the individual features.
% Continuing the line of examples started before, we again use an example
% about sections -- just now with an environment for section boxes, as
% provided by the \textsf{sectionbox} package.
%
% \SaveSecs
% \begin{LTXexample}[morekeywords={NewMultilangEnv}]
% \usepackage{sectionbox}
% \NewMultilangEnv{SecBox}{
%   environment=sectionbox,
%   disablable, margs=title, oargs=width}
%
% \begin{SecBox}{title=Foo}
%   content
% \end{SecBox}
%
% \begin{SecBox}{disabled,title=Bar}
%   disabled content
% \end{SecBox}
% \end{LTXexample}
% \RestoreSecs
%
%
% \section{Extensible Argument Types}
% \label{sec:Types}
%
% By default, an argument |arg| in a multilingual macro can be specified in
% three ways: just ``|arg=...|'', ``|arg/|\meta{language}|=...|'', or
% ``|arg/|\meta{language}|!=...|''.
% The \ThisPackage package enables one to declare further so called `types'.
% These types can be used in place of \meta{language} in the argument syntax.
% They can be used for uniformly enabling a special formatting if an argument
% is of a particular type (rather than just being text).
%
% \NiceDescribeMacro{\NewMultilangType}{\oarg{argcount}\marg{typename}\marg{format}}
% The |\NewMultilangType| macro declares the \meta{typename} type.
% Values passed to arguments of this type must consist of \meta{argcount}
% arguments (default: 1). The value is then formatted with \meta{format} when
% displayed. The \meta{format} can (and should) contain positional parameters
% such as ``|#1|'' for the first argument.
% The remainder of this \lcnamecref{sec:Types} demonstrates the use of
% the macro by examples.
%
%
% \subsection{Dates via \textsf{datetime2}}
%
% The \textsf{datetime2} package supports regional (language-specific)
% formatting of dates. We can build on this feature such that we don't
% have to provide translations of dates. To keep the display
% smaller, we here use |\textbf| rather than |\section|.
%
% \begin{LTXexample}[morekeywords={NewMultilangType,date,daterange}]
% \usepackage[useregional]{datetime2}
%
% \NewMultilangType{date}{\DTMdate{#1}}
% \NewMultilangType[2]{daterange}
%    {\DTMdate{#1}--\DTMdate{#2}}
%
% \NewMultilangCmd{\Bold}
%    {margs=title, command=\textbf}
%
% Date:  \Bold{title/date={2017-08-01}}\\
% Range: \Bold{title/daterange=
%          {2017-01-01}{2017-08-01}}
% \end{LTXexample}
%
%
% \subsection{Nesting Multilingual Macros}
%
% Multilingual macros can be used in arguments to multilingual macros.
% Coming back to the original motivation for developing \ThisPackage
% -- CVs -- you might want a translated two-column layout in which the
% right column might be filled with translated list items. The following
% example shows how this can be realized.
%
% \begin{LTXexample}
% \usepackage{enumitem}% for "nosep"
%
% \newcommand\entry[2]{%
%    \begin{tabular}{p{1cm}p{4cm}}#1&#2
%    \end{tabular}}
%
% \NewMultilangType{list}{%
%    \begin{minipage}[t]{4cm}
%    \begin{itemize}[nosep]#1
%    \end{itemize}\end{minipage}}
% \NewMultilangCmd{\Entry}
%    {margs={head,text}, command=\entry}
% \NewMultilangCmd{\Item}
%    {margs=name, command=\item}
%
% \Entry{head=2017,
%   text/list={
%     \Item{name/english=foobar,
%           name/german =Dingsda}
%     \Item{name=multilang}}}
% \end{LTXexample}
%
%
% \section{Extension Packages}
% \label{sec:Extensions}
%
% The \ThisPackage package comes bundled with a few generic packages that build
% on \ThisPackage. These packages are described below.
%
% \subsection{Sectioning Environments}
%
% Sectioning environments are provided by the \textsf{multilang-sect} package.
% That package defines, for each of \LaTeX's sectioning macros (|\section|,
% \ldots, |\subparagraph|) an environment and a starred environment.
%
% \NiceDescribeEnv[Section,Section*]{Section(*)}{\marg{data}}
% This environment shows a section.
% It has a single, mandatory argument, named |title|.
% It is a disablable environment, i.e., the argument |disabled| can be used in
% \meta{data} to disable the display of the whole section.
% This environment acts as a proxy for the |\section| macro as it is used by
% \ThisPackage (i.e., without optional argument and without the star).

% \NiceDescribeEnv[SubSection,SubSection*]{SubSection(*)}{\marg{data}}
% This environment is analogous to the |Section| environment, just for
% sub-sections.

% \NiceDescribeEnv[SubSubSection,SubSubSection*]{SubSubSection(*)}{\marg{data}}
% This environment is analogous to the |Section| environment, just for
% sub-sub-sections.

% \NiceDescribeEnv[Paragraph,Paragraph*]{Paragraph(*)}{\marg{data}}
% This environment is analogous to the |Section| environment, just for
% paragraphs.

% \NiceDescribeEnv[SubParagraph,SubParagraph*]{SubParagraph(*)}{\marg{data}}
% This environment is analogous to the |Section| environment, just for
% sub-paragraphs.
% Examples:
%
% \SaveSecs
% \begin{LTXexample}[morekeywords={Section,SubSection}]
% \usepackage{multilang-sect}
%
% \begin{Section}{
%     title/english = Usage,
%     title/german  = Benutzung,
%   }
%   (section content)
%   \begin{SubSection*}{
%       title/english = Package Options,
%       title/german  = Paketoptionen,
%     }
%     (subsection content)
%   \end{SubSection*}
% \end{Section}
% \end{LTXexample}
% \RestoreSecs
%
%
% \subsection{Tags}
%
% Tags are an alternative to individually disabling macros or environments.
% They are provided by the \textsf{multilang-tags} package.
% A tag is just a word and sets of tags can be assigned to individual usages of
% multilingual macros and environments.
% As long as no tag filter policy is setup, specifying tags does not influence
% what is displayed.
%
% \NiceDescribeMacro{\SetTagFilter}{\oarg{default}\marg{policy}}
% The |\SetTagFilter|\oarg{default}\marg{policy} sets up a tag filter policy.
% The \meta{policy} is a comma-separated list of |accept|/|deny| rules.
% The \meta{default} argument is either |accept| (the default) or |deny| and
% specifies the default policy.
% The following toy example demonstrates tag filtering:
% 
% \begin{LTXexample}[morekeywords={SetTagFilter,tags}]
% \usepackage{multilang-tags}
% \NewMultilangCmd{\Item}{disablable,
%   command=\item,oargs=dd,margs=dt,
%   alias/both={dd,dt}}
% \SetTagFilter{accept={A}, deny={D}}
%
% \begin{description}
% \Item{tags=A,     both={1}{tagged A}}
% \Item{tags={A,D}, both={2}{tagged A,D}}
% \Item{tags=D,     both={3}{tagged D}}
% \Item{tags={D,X}, both={4}{tagged D,X}}
% \Item{tags=!D,    both={5}{tagged !D}}
% \Item{tags=X,     both={6}{tagged X}}
% \end{description}
% \end{LTXexample}
%
% When a multilingual macro, such as |\BasicEntry| in the above example, is
% used, whether the macro content is displayed is determined as follows:
% \begin{itemize}[nosep]
% \item If no |tags| are specified or no tag policy is setup, then the macro
%   content is displayed.
% \item Otherwise, the rules of the tag policy are processed in sequential order
%   until the specified |tags| match a rule.
%   A |tags| list matches a rule if at least one tag in the |tags| occurs in the
%   rule (with or without ``|!|'' prefix).
%   Let $t$ be the last tag in |tags| that occurs in the rule.
%   \begin{itemize}[nosep]
%   \item The macro content is displayed if the rule is an |accept| rule and $t$
%     is not prefixed with ``|!|'', or if the rule is a |deny| rule and $t$ is
%     prefixed with ``|!|''.
%   \item Otherwise the display of the macro content is disabled.
%   \end{itemize}
% \item If the specified |tags| match no rule in the \meta{policy}, then the
%   macro content is displayed if and only if the \meta{default} is |accept|.
% \end{itemize}
%
% Rather than directly setting up a filter policy, one can also use the
% following macros to first define filter policies and then select one for use.
%
% \NiceDescribeMacro{\DefineTagFilter}{\marg{name}\marg{default}\marg{policy}}
% This macro defines a tag filter policy with name \meta{name} to represent the
% given \meta{policy} and \meta{default}.
%
% \NiceDescribeMacro{\UseTagFilter}{\marg{name}}
% This macro uses the tag filter policy with name \meta{name}.
%
% Further examples:
% \begin{LTXexample}[morekeywords={DefineTagFilter,UseTagFilter,tags},preset={\NewMultilangCmd{\Item}{disablable,command=\item,oargs=dd,margs=dt,alias/both={dd,dt}}}]
% \DefineTagFilter{Show}{accept}{}
% \DefineTagFilter{Hide}{deny}{}
% \DefineTagFilter{OnlyA}{accept}{accept=A,
%                                 deny={D,X}}
% \begin{description}
% \UseTagFilter{Hide}
% \Item{            both={1}{no tag}}
% \Item{tags=D,     both={2}{tagged D}}
% \UseTagFilter{OnlyA}
% \Item{tags={D,!X},both={3}{tagged D,!X}}
% \Item{tags={!X,D},both={4}{tagged !X,D}}
% \end{description}
% \end{LTXexample}
%
%
% \section{Questions and Answers}
%
% \begin{description}
% \item[Can't I achieve the same thing simpler?]
%   To some extent, you can.
%   A variety of ad-hoc solutions to managing translations in \LaTeX{}
%   documents exist.\footnote{see, e.g.,
%   \url{https://tex.stackexchange.com/q/5076}}
%   An obvious approach is the following:
%   \SaveSecs
%   \begin{LTXexample}
% \newcommand\inEnglish[1]{#1}
% \newcommand\inGerman[1]{}
%
% \inEnglish{\section{Foobar}}
% \inGerman{\section{Dingsda}}
% % or
% \section{\inEnglish{Foobar}
%          \inGerman{Dingsda}}
%   \end{LTXexample}
%   \RestoreSecs
%   That is, for each translation language you define a macro with one
%   argument; the macro for the ``selected'' language expands to the argument
%   while all other macros have an empty expansion.
%   An obvious advantage of this approach over \ThisPackage is that it does
%   not require learning how to use \ThisPackage.
%   However, in my opinion, the approach has the following disadvantages:
%   \begin{itemize}[nosep]
%   \item Both the first variant and the second variant in the example make
%     the code more difficult to read due to the nesting of macros and the
%     curly braces.
%   \item The first variant even requires the |\section| macro to be repeated
%     for each language.
%   \item The second variant easily gets chaotic if instead of |\section| a
%     macro with several arguments is used.
%   \end{itemize}
%   Solutions with conditionals (e.g., |\ifEnglish ...\else ...\fi|) share the
%   disadvantages of above approach (except the curly braces) and additionally
%   have an inherent asymmetry that becomes particularly apparent if more than
%   two languages are involved.
%   Similar arguments apply to other ad-hoc solutions I have seen.
%   That is, I find documents based on such approaches cumbersome to maintain
%   and, hence, requiring more careful checks for ensuring consistency.
%   
% \item[Can I use \ThisPackage with \textsf{polyglossia} instead of \textsf{babel}?]
%   Yes, you can use either one for selecting the language of your document.
%
% \item[Can I switch the language mid-document?]
%   You can switch the language mid-document (e.g., using Babel's
%   |selectlanguage| environment), but this does not effect what the
%   multilingual macros or environments defined via \ThisPackage.
%   The language that is displayed by a macro or environment is determined at
%   the time of loading \ThisPackage.
%   Future versions of \ThisPackage might add support for switching languages
%   mid-document, though.
%
% \item[Are language dialects supported?]
%   No, currently they are not supported.
%
% \item[Can I store the ``result'' of a multilingual macro in another macro?]
%   No.
%   You can store the macro itself (e.g., via |\newcommand|), but storing the
%   result of the multilingual macro in a macro (e.g., via |\edef|) is not
%   possible, as the multilingual macros are not expandable.
% \end{description}
%
%
% \section{Related Packages}
%
% I'm not aware of any \LaTeX{} packages that pursue similar goals or
% provide similar functionality.
% CTAN provides a list of many packages for supporting more than one
% language.\footnote{\url{https://www.ctan.org/topic/multilingual}}
% In the following, we compare against some of these packages.
%
% \begin{description}
% \item[\textsf{babel}, \textsf{polyglossia}:]
%   These package provide support for selecting a document language and
%   switching the document language within a document. The selected language
%   is then used for hyphenation and other layouting aspects.
%   Providing multiple translations of pieces of content is not particularly
%   facilitated by the two packages.
%
%   The \ThisPackage package builds on \textsf{babel} or \textsf{polyglossia}
%   for determining the selected language and for forced foreign-language
%   formatting (as illustrated in \cref{sec:Usage-margs}).
%
% \item[\textsf{translations}:]
%   This package aims primarily aims at package authors, providing them an
%   easy interface for providing translations of package-specific terms.
%   Essentially, one declares translations for terms up-front and then later
%   can use these translations.
%
%   The separation of translations and the use of terms is beneficial
%   for the maintenance of packages and documents in which individual terms
%   occur multiple times. However, I assume that this separation would make it
%   harder to maintain documents in which most translated units occur only
%   once and at a particular location in the document.
%
%   One could combine the virtues of \textsf{translations} and \ThisPackage as
%   follows:
%   \SaveSecs
%   \begin{LTXexample}[morekeywords={DeclareTranslation,GetTranslation},preset={\let\DeclareTranslation=\addtranslation}]
% % in preamble
% \usepackage{translations}
% \DeclareTranslation{english}{foo}{Foobar}
% \DeclareTranslation{german}{foo}{Dingsda}
% \NewMultilangType{translate}
%                  {\GetTranslation{#1}}
% \NewMultilangCmd{\Sec}{
%    margs=title, command=\section}
%
% % in document
% \Sec{title/translate=foo}
%   \end{LTXexample}
%   \RestoreSecs
%
% \item[\textsf{xt\_capts}:]
%   This package is similar to the \textsf{translations} package, even though
%   the package's documentation does not explicitly refer to package authors
%   as the target users. That is, it provides commands for declaring and using
%   translations of terms.
%   The main difference to \textsf{translations}, as far as I understand, is
%   that the user interface of \textsf{translations} is larger and supports
%   language dialects.
%   Comparing with \ThisPackage, the same remarks as for \textsf{translations}
%   apply.
% \end{description}
%
%
% \clearpage
%
% \StopEventually{}
%\iffalse
%<*package>
%\fi
%
%
% \section{Implementation}
%
% \subsection{Dependencies}
%
% We use \textsf{pgfkeys} for the options parsing, both for the macros defined
% by \ThisPackage and for the macro defined via the macros in \ThisPackage.
% We use \textsf{etoolbox} to simplify the internal code.
%    \begin{macrocode}
\RequirePackage{pgfkeys,pgfopts}
\RequirePackage{etoolbox}
%    \end{macrocode}
% We use the \textsf{environ} package for scanning and later forgetting the
% body of disabled multilingual environments.
%    \begin{macrocode}
\RequirePackage{environ}
%    \end{macrocode}
%
%
% \subsection{Package Options}
%
% The ``|languages|'' option selects the languages that \ThisPackage knows
% about.
%    \begin{macrocode}
\newcommand\multilang@@langs{}
\pgfqkeys{/multilang/pkg}{
  languages/.code={\forcsvlist{\listadd\multilang@@langs}{#1}},
}
\ProcessPgfOptions{/multilang/pkg}
%    \end{macrocode}
%
% \subsection{Main Macros}
%
% \begin{macro}{\NewMultilangCmd}
% The |\NewMultilangCmd|\marg{command}\marg{options} macro defines
% \meta{command} to be a single-argument macro. The argument to \meta{command}
% specifies, in a key-value list style, the mandatory and optional arguments
% that are passed to a command specified in \meta{options}.
%    \begin{macrocode}
\newcommand\NewMultilangCmd[2]{%
  \bgroup
%    \end{macrocode}
% The following line processes the \meta{options} given and, as its result,
% defines the macros
% |\multilang@@actuals|, |\multilang@@checks|, and |\multilang@@keys|.
%    \begin{macrocode}
  \multilang@processargs{#1}{/multilang/newcommand}{defaults={},#2}%
%    \end{macrocode}
% To handle starred macros, we store the actual macro code into an auxiliary
% macro and define \meta{command} to be an interface to the auxiliary macro.
% The next line stores the name of the internal macro.
%    \begin{macrocode}
  \expandafter\def\expandafter\multilang@@intcmd\expandafter{%
    \csname multilang@intcmd@\expandafter\@gobble\string#1\endcsname}%
%    \end{macrocode}
% Finally, we create the \meta{command}. The |\edef| starting with the
% |\egroup| shall expand the three macros constructed above but nothing else
% such that none of the |\pgfqkeys| result for |#1| spills outside the
% |\NewMultilangCmd|.
%    \begin{macrocode}
  \edef\do{\egroup
    \expandonce{\multilang@@keys}%
    \ifbool{multilang@@starred}{%
%    \end{macrocode}
% The following handles the case of a |starred| macro. We define the macro
% that scans for the star (\meta{command}) as well as the internal macro that
% does the actual work.
%    \begin{macrocode}
      \unexpanded{\newcommand#1}{%
        \noexpand\@ifstar
          {\expandonce{\multilang@@intcmd}{*}}%
          {\expandonce{\multilang@@intcmd}{}}}%
    }{%
%    \end{macrocode}
% The following handles the case of a non-|starred| macro. Here we make
% \meta{command} directly resort to the internal macro.
%    \begin{macrocode}
      \unexpanded{\newcommand#1}{\expandonce{\multilang@@intcmd}{}}%
    }%
%    \end{macrocode}
% The remainder of the macro code defines the internal macro, with signature
% \meta{\cs{multilang@@keys}}\marg{decoration}\marg{kvarg}.
% The \meta{decoration} can assume any symbols that shall directly be put
% after the command encapsulated by |command|. A particular use for the
% \meta{decoration} argument is the ``|*|'' symbol for a |starred| macro.
%    \begin{macrocode}
    \noexpand\newcommand{\expandonce{\multilang@@intcmd}}[2]{%
%    \end{macrocode}
% First, \meta{command} parses its argument using \textsf{pgfkeys}.
%    \begin{macrocode}
      \bgroup
      \noexpand\boolfalse{multilang@cmd@@disabled}%
      \noexpand\pgfqkeys{\multilang@keyof{#1}}{%
        \expandonce{\multilang@@defaults},####2}%
      \noexpand\ifbool{multilang@cmd@@disabled}%
%    \end{macrocode}
% If the macro is disabled, simply use an empty invocation
% |\multilang@@invok|.
%    \begin{macrocode}
        {\unexpanded{\def\multilang@@invok{}}}%
%    \end{macrocode}
% Otherwise, first check the arguments and afterwards define
% |\multilang@@invok| to contain \meta{command}, \meta{decoration} (in
% |####1|), and the actual arguments (in |\multilang@@actuals|).
%    \begin{macrocode}
        {\expandonce{\multilang@@checks}%
          \unexpanded{\edef\multilang@@invok}{%
            \noexpand\unexpanded{\expandonce{\multilang@@cmd}}####1%
              \expandonce{\multilang@@actuals}}}%
%    \end{macrocode}
% Finally, \meta{command} invokes the command specified via the |command| key.
% The invocation happens outside the local group, just for the case that makes
% a difference with the |command|.
%    \begin{macrocode}
      \unexpanded{\expandafter\egroup\multilang@@invok}%
    }%
  }\do}
%    \end{macrocode}
%
%
% \begin{macro}{\NewMultilangEnv}
% The |\NewMultilangEnv|\marg{environment}\marg{options} macro defines
% \meta{environment} to be a single-argument environment. The argument to
% \meta{environment} specifies, in a key-value list style, the mandatory and
% optional arguments that are passed to an environment specified in
% \meta{options}.
%    \begin{macrocode}
\newcommand\NewMultilangEnv[2]{%
  \bgroup
%    \end{macrocode}
% The following line processes the \meta{options} given and, as its result,
% defines the macros
% |\multilang@@actuals|, |\multilang@@checks|, and |\multilang@@keys|.
%    \begin{macrocode}
  \multilang@processargs{#1}{/multilang/newenvir}{defaults={},#2}%
%    \end{macrocode}
% Finally, we create the \meta{environment}. The |\edef| starting with the
% |\egroup| shall expand the three macros constructed above but nothing else
% such that none of the |\pgfqkeys| result for |#1| spills outside the
% |\NewMultilangEnv|. We also pay attention that as few as possible internal
% macros spill into the environment or even the code that begins the
% environment.
%    \begin{macrocode}
  \edef\do{\egroup
    \expandonce{\multilang@@keys}%
    \unexpanded{\newenvironment{#1}}[1]{%
%    \end{macrocode}
% First, \meta{command} parses its argument using \textsf{pgfkeys}.
%    \begin{macrocode}
      \bgroup
      \noexpand\boolfalse{multilang@cmd@@disabled}%
      \noexpand\pgfqkeys{\multilang@keyof{#1}}{####1}%
      \noexpand\ifbool{multilang@cmd@@disabled}%
%    \end{macrocode}
% If the body shall be disabled, then we don't perform checks on the
% arguments, don't open |environment| but rather collect the body of the
% environment and finally also ignore the code for closing |environment| (via
% |\multilang@noend|). Through this trick, we avoid defining an additional
% macro for switching in the end-block of the environment.
%    \begin{macrocode}
        {\unexpanded{%
          \def\multilang@@invok{\Collect@Body{\multilang@noend}}}}%
%    \end{macrocode}
% First check the arguments and afterwards define
% |\multilang@@invok| to contain the opening code for the environment,
% including the actual arguments (in |\multilang@@actuals|).
%    \begin{macrocode}
        {\expandonce{\multilang@@checks}%
        \unexpanded{\edef\multilang@@invok}{%
          \noexpand\noexpand\noexpand\begin{\multilang@@env}%
            \expandonce{\multilang@@actuals}}}%
%    \end{macrocode}
% Finally, \meta{environment} begins the environment specified via the
% |environment| key. This happens outside the local group, such that the
% internal macros set via |\pgfqkeys| are not visible anymore when the
% environment is started.
%    \begin{macrocode}
      \unexpanded{\expandafter\egroup\multilang@@invok}%
    }{%
%    \end{macrocode}
% The following implements the closing of the environment.
%    \begin{macrocode}
      \noexpand\end{\multilang@@env}%
    }%
  }\do}
%    \end{macrocode}
%
%
% \subsubsection{Option Keys}
%
% We first setup the shared keys for the \meta{options} argument of
% |\NewMultilangCmd| and |\NewMultilangEnv|.
%    \begin{macrocode}
\pgfqkeys{/multilang/cmd-or-env}{
  margs/.store in={\multilang@@margs},
  oargs/.store in={\multilang@@oargs},
  alias/.is family,
  alias/.unknown/.code={%
    \listeadd{\multilang@@aliases}{\pgfkeyscurrentname}%
    \csdef{multilang@@alias@\pgfkeyscurrentname}{#1}},
  defaults/.store in={\multilang@@defaults},
  disablable/.is if={multilang@@disablable},
}
\newbool{multilang@@disablable}
\newbool{multilang@cmd@@disabled}
%    \end{macrocode}
%
% Next, we setup the specific keys for |\NewMultilangCmd|.
%    \begin{macrocode}
\pgfqkeys{/multilang/newcommand}{
  .search also={/multilang/cmd-or-env},
  command/.store in={\multilang@@cmd},
  starred/.is if={multilang@@starred},
  alias/.search also={/multilang/cmd-or-env},
}
\newbool{multilang@@starred}
%    \end{macrocode}
% \end{macro}
% Finally, the specific keys for |\NewMultilangEnv|.
%    \begin{macrocode}
\pgfqkeys{/multilang/newenvir}{
  .search also={/multilang/cmd-or-env},
  environment/.store in={\multilang@@env},
  alias/.search also={/multilang/cmd-or-env},
}
%    \end{macrocode}
% \end{macro}
%
%
% \subsection{Registration of Datatypes}
%
% \begin{macro}{\NewMultilangType}
% The |\NewMultilangType|\oarg{argcount}\marg{typename}\marg{format} macro
% registers the name \meta{typename} as a type that can be used for specifying
% \ThisPackage arguments. The type has \meta{argcount} arguments (default: 1)
% and is formatted according to code \meta{format}.
% Note that the definition of types is group-local. That is, if
% |\NewMultilangType| is used within a group, \meta{typename} is only
% available inside that group.
%    \begin{macrocode}
\newcommand\NewMultilangType[3][1]{%
%    \end{macrocode}
% We first record the new type's name (in |\multilang@@types|) and store both
% \meta{argcount} and \meta{format} in macros.
%    \begin{macrocode}
  \listadd\multilang@@types{#2}%
  \expandafter\newcommand\csname multilang@@typecmd@#2\endcsname[#1]{#3}%
  \csdef{multilang@@typeargc@#2}{#1}%
%    \end{macrocode}
% Finally, we also store the invocation of the \meta{format} code macro.
% This is a bit cumbersome, as for all possible argument counts we provide the
% respective number of arguments. I did not yet find a more elegant way to
% achieve that the |style n args| code in |\multilang@regfieldtype| invokes
% \meta{format} properly with \meta{argcount} arguments.
% \meta{argcount} and \meta{format} in macros.
%    \begin{macrocode}
  \ifcase#1\relax
     \csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}}%
%    \end{macrocode}
% For one argument, we check a special case: \meta{format} is the identity
% function. In this case, we directly expand to the argument itself, i.e., we
% unfold \meta{format}. We do this such that emptiness of optional arguments
% can be checked by a |command| or |environment| without having to expand the
% \meta{format} (which might not work out if \meta{format} is not expansible).
% For instance, KOMA's |\section| macro hides the TOC entry for
% |\section[]{...}| but not for |\section[\X]{...}| even if |\X| expands to an
% empty result.
%    \begin{macrocode}
  \or\ifcsequal{multilang@@typecmd@#2}{@firstofone}%
    {\csdef{multilang@@runcmd@#2}{####1}}%
    {\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}{####3}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}{####3}{####4}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}{####3}{####4}{####5}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}{####3}{####4}{####5}{####6}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}{####3}{####4}{####5}{####6}{####7}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}{####3}{####4}{####5}{####6}{####7}{####8}}%
  \or\csdef{multilang@@runcmd@#2}{\csuse{multilang@@typecmd@#2}%
      {####1}{####2}{####3}{####4}{####5}{####6}{####7}{####8}{####9}}%
  \else\multilang@error{Argument count expected to be between 0 and 9, %
                        but is '#1'}\fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@@types}
% The |\multilang@@types| macro collects and holds an \textsf{etoolbox} list
% of datatypes defined via |\NewMultilangType|.
%    \begin{macrocode}
\newcommand\multilang@@types{}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\NewMultilangType@code}
% The |\NewMultilangType@code|\oarg{argcount}\marg{typename}\marg{format}
% macro is an internal counterpart to |\NewMultilangType| with which not
% not the |.style| but the |.code| property of the \meta{typename} key is
% defined. This is indicated by defining the
% |\multilang@@codetype@|\meta{typename} macro here and checking whether this
% macro is defined in |\multilang@regfieldtype|.
%    \begin{macrocode}
\newcommand\NewMultilangType@code[3][1]{%
  \csdef{multilang@@codetype@#2}{true}%
  \NewMultilangType[#1]{#2}{#3}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@regfield}
% The |\multilang@regfield|\marg{cmd-or-env}\marg{fieldname} macro registers
% the respective \textsf{pgfkeys} keys for \meta{fieldname} for all registered datatypes.
%    \begin{macrocode}
\newcommand\multilang@regfield[2]{%
  \pgfqkeys{\multilang@keyof{#1}}{%
    #2/.code={\csdef{multilang@@val@#2}{##1}}}%
  \forlistloop{\multilang@regfieldtype{#1}{#2}}{\multilang@@types}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@regfieldtype}
% The |\multilang@regfieldtype|\marg{cmd-or-env}\marg{fieldname}\marg{typename}
% macro registers the \textsf{pgfkeys} key for \meta{typename} of
% \meta{fieldname}.
%    \begin{macrocode}
\newcommand\multilang@regfieldtype[3]{%
  \bgroup
%    \end{macrocode}
% In the following, we check whether the number of arguments for the
% \meta{typename} macro is 1, because for some reason |style n args| seems not
% to work as we want it to work if $n=1$.
%    \begin{macrocode}
  \ifnumequal{\csuse{multilang@@typeargc@#3}}{1}{%
    \ifcsdef{multilang@@codetype@#3}{%
      \edef\do{\egroup\noexpand\pgfqkeys{\multilang@keyof{#1}}{%
        #2/#3/.code={\csexpandonce{multilang@@runcmd@#3}}%
      }}%
    }{%
      \edef\do{\egroup\noexpand\pgfqkeys{\multilang@keyof{#1}}{%
        #2/#3/.style={#2={\csexpandonce{multilang@@runcmd@#3}}}%
      }}%
    }%
  }{%
    \ifcsdef{multilang@@codetype@#3}{%
      \edef\do{\egroup\noexpand\pgfqkeys{\multilang@keyof{#1}}{%
        #2/#3/.code n args={\csuse{multilang@@typeargc@#3}}%
                           {\csexpandonce{multilang@@runcmd@#3}}}}%
    }{%
      \edef\do{\egroup\noexpand\pgfqkeys{\multilang@keyof{#1}}{%
        #2/#3/.style n args={\csuse{multilang@@typeargc@#3}}%
                           {#2={\csexpandonce{multilang@@runcmd@#3}}}}}%
    }%
  }\do}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{Argument Aliases}
%
% \begin{macro}{\multilang@regcomb}
% The |\multilang@regcomb|\marg{cmd-or-env}\marg{alias}\marg{fields}
% macro registers an \meta{alias} argument for \meta{fields}.
%    \begin{macrocode}
\newcommand\multilang@regcomb[3]{%
  \multilang@regcombtype{#1}{#2}{#3}{}%
  \forlistloop{\multilang@regcomb@i{#1}{#2}{#3}}{\multilang@@types}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@regcomb@i}
% The
% |\multilang@regcomb@i|\marg{cmd-or-env}\marg{alias}\marg{fields}\marg{type}
% macro is an auxiliary front-end to |\multilang@regcombtype| that transforms
% \meta{type} to a key \meta{suffix} (by prepending a ``|/|'').
%    \begin{macrocode}
\newcommand\multilang@regcomb@i[4]{%
  \multilang@regcombtype{#1}{#2}{#3}{/#4}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@regcombtype}
% The
% |\multilang@regcombtype|\marg{cmd-or-env}\marg{alias}\marg{fields}\marg{suffix}
% registers the \meta{alias} with the given type-\meta{suffix}.
%    \begin{macrocode}
\newcommand\multilang@regcombtype[4]{%
  \bgroup
%    \end{macrocode}
% We count the number of field names in \meta{fields} (in |\@tempcnta|) and,
% in the same loop, gather the individual field assignments (in |\toks@|).
%    \begin{macrocode}
  \toks@{}\@tempcnta=0\relax
  \forcsvlist{%
    \advance\@tempcnta by1\relax
    \expandafter\multilang@regcomb@set\expandafter{\the\@tempcnta}{#4}%
  }{#3}%
%    \end{macrocode}
% Finally, we set the style for the \meta{alias}\meta{suffix} key. Again we
% separately handle the case of a single field. Additionally, we treat also
% the case of \emph{no} field special: It gets a |style| (with 1 argument),
% but the argument is essentially ignored (as |\toks@| is empty). This makes
% \meta{alias} a ``comment'' field that is not passed to the |command| or
% |environment|.
%    \begin{macrocode}
  \ifnumgreater{\the\@tempcnta}{1}{%
    \edef\do{\egroup\noexpand\pgfqkeys{\multilang@keyof{#1}}{%
      #2#4/.style n args={\the\@tempcnta}{\the\toks@}}}%
  }{%
    \edef\do{\egroup\noexpand\pgfqkeys{\multilang@keyof{#1}}{%
      #2#4/.style={\the\toks@}}}%
  }%
  \do}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@regcomb@set}
% The |\multilang@regcomb@set|\marg{index}\marg{suffix}\marg{field} macro
% appends the sequence ``\meta{field}\meta{suffix}|={#|\meta{index}|}|'' to
% the |toks@| register.  When used in a |.style n args| key, this sets the
% ``\meta{field}\meta{suffix}'' key to the \meta{index}-th positional
% parameter.
%    \begin{macrocode}
\newcommand\multilang@regcomb@set[3]{%
  \toks@\expandafter{\the\toks@,#3#2={###1}}}
%    \end{macrocode}
% \end{macro}
%
%
% \subsubsection{Language ``Types''}
%
% \begin{macro}{\multilang@addlanguage}
% The |\multilang@addlanguage|\marg{language} registers \meta{language},
% essentially registering ``\meta{language}'' and ``\meta{language}|!|'' as
% argument datatypes.
%    \begin{macrocode}
\newcommand\multilang@addlanguage[1]{%
%    \end{macrocode}
% The following checks the current language (|\languagename|) against
% \meta{language}. In the following,
% |##1| is the argument to the key when the key is used.
%    \begin{macrocode}
  \ifdefstring{\languagename}{#1}%
    {\NewMultilangType{#1}{##1}}%
    {\NewMultilangType@code{#1}{}}%
%    \end{macrocode}
% The following defines the ``\meta{language}|!|'' key for forcing an
% argument to be formatted in language \meta{language}.
%    \begin{macrocode}
  \NewMultilangType{#1!}{\foreignlanguage{#1}{##1}}}
%    \end{macrocode}
% \end{macro}
% Register all languages passed as argument to the package.
%    \begin{macrocode}
\forlistloop{\multilang@addlanguage}{\multilang@@langs}
%    \end{macrocode}
%
%
% \subsection{Auxiliary Macros}
%
% \begin{macro}{\multilang@keyof}
% The |\multilang@keyof|\marg{cmd-or-env}, when fully expanded such as in the
% first argument of the |\pgfqkeys| macro, represents the key under which the
% parameter keys of the command or environment \meta{cmd-or-env} are stored.
% Note that the branching in the code below checks whether \meta{cmd-or-env}
% is a command sequence (|true| case) or not (|false| case).
%    \begin{macrocode}
\newcommand\multilang@keyof[1]{%
  \ifcat\relax\noexpand#1%
    /multilang/cmd/\expandafter\@gobble\string#1%
  \else
    /multilang/env/#1%
  \fi}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@error}
% The |\multilang@error|\marg{message} macro shows \meta{message} as an error
% message of the \ThisPackage package.
%    \begin{macrocode}
\newcommand\multilang@error[1]{\PackageError{multilang}{#1}{}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@processargs}
% The |\multilang@processargs|\marg{cmd-or-env}\marg{opt-key}\marg{options}
% macro processes the \meta{options} in key \meta{opt-key}. Afterwards, it
% post-processes the arguments |margs|, |oargs|, |alias/...|, and
% |disablable|.
% It stores the result of the post-processing in the macros
% |\multilang@@actuals|, |\multilang@@checks|, and |\multilang@@keys|.
%    \begin{macrocode}
\newcommand\multilang@processargs[3]{%
  \let\multilang@@aliases=\empty
  \pgfqkeys{#2}{#3}%
%    \end{macrocode}
% In the following, we iteratively construct three macros:
% |\multilang@@actuals|, |\multilang@@checks|, and |\multilang@@keys|.
% \begin{itemize}[nosep]
% \item In |\multilang@@actuals|, we step by step construct the arguments that
%   shall be passed to \meta{cmd-or-env}.
% \item In |\multilang@@checks|, we construct a list of preliminary checks
%   that \meta{cmd-or-env} shall perform on its arguments.
% \item In |\multilang@@keys|, we construct a list of |\pgfqkeys| commands
%   that set up the keys for \meta{cmd-or-env}'s one argument.
% \end{itemize}
% The following first initializes the three macros.
%    \begin{macrocode}
  \edef\multilang@@actuals{}%
  \def\multilang@@checks{}%
  \def\multilang@@keys{}%
%    \end{macrocode}
% We first process the optional arguments. We process them before the
% mandatory arguments because they must come first in |\multilang@@actuals|.
% In the following |\do| macro, |##1| iterates over all optional argument
% names in the |margs| list.
%    \begin{macrocode}
  \ifdefvoid{\multilang@@oargs}{}{%
    \def\do##1{%
      \appto{\multilang@@actuals}{%
        \ifcsmacro{multilang@@val@##1}%
          {[\csexpandonce{multilang@@val@##1}]}%
          {}%
      }%
      \appto{\multilang@@keys}{\multilang@regfield{#1}{##1}}%
    }%
    \expandafter\docsvlist\expandafter{\multilang@@oargs}}%
%    \end{macrocode}
% Next, we append the mandatory arguments, specified by the |margs| list.
% In the following |\do| macro, |##1| iterates over all mandatory argument
% names in the |margs| list.
%    \begin{macrocode}
  \ifdefvoid{\multilang@@margs}{}{%
    \def\do##1{%
      \appto{\multilang@@actuals}{%
        {\csexpandonce{multilang@@val@##1}}%
      }%
      \appto{\multilang@@checks}{%
        \ifcsmacro{multilang@@val@##1}%
          {}%
          {\multilang@error{mandatory argument ##1 missing}}%
      }%
      \appto{\multilang@@keys}{\multilang@regfield{#1}{##1}}%
    }%
    \expandafter\docsvlist\expandafter{\multilang@@margs}}%
%    \end{macrocode}
% Afterwards, we handle argument aliases. The list of aliases' names is in
% |\multilang@@aliases| and the list of arguments that a \meta{alias}
% combines is in |\multilang@@alias@|\meta{alias}.
% Note that aliases only modify |\multilang@@keys| -- i.e., not
% |\multilang@@actuals| or |\multilang@@checks|.
%    \begin{macrocode}
  \def\do##1{%
    \eappto{\multilang@@keys}{%
      \unexpanded{\multilang@regcomb{#1}{##1}}%
        {\csuse{multilang@@alias@##1}}}}%
  \expandafter\dolistloop\expandafter{\multilang@@aliases}%
%    \end{macrocode}
% To handle |disablable| macros, we simply add the |disabled| key. This key is
% a Boolean key that just sets a conditional.
%    \begin{macrocode}
  \ifbool{multilang@@disablable}%
    {\eappto{\multilang@@keys}{%
      \noexpand\pgfqkeys{\multilang@keyof{#1}}{%
        disabled/.is if={multilang@cmd@@disabled}}}}%
    {}%
%    \end{macrocode}
% Invoke the hook. To avoid macro arguments to the hook, we store the command or
% environment name in |\multilang@@cmdorenv| and store the \textsf{pgfkeys} key
% for the command or environment in |\multilang@@cekey|.
%    \begin{macrocode}
  \def\multilang@@cmdorenv{#1}%
  \edef\multilang@@cekey{\multilang@keyof{#1}}%
  \multilang@hook@processargs
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@hook@processargs}
% The |\multilang@hook@processargs| macro is a hook that enables extensions to
% the |\multilang@processargs|.
%    \begin{macrocode}
\newcommand\multilang@hook@processargs{}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\multilang@noend}
% The |\multilang@noend|\marg{body} macro is intended to be used as the
% argument to |\Collect@Body| (or |\collect@body|) of the \textsf{environ}
% package. In this context, it performs the following:
% Firstly, it ignores the collected \meta{body} of the environment.
% Secondly, it temporarily disables the |\end|-code of the environment in
% which the |\Collect@Body| is expanded.
%    \begin{macrocode}
\newcommand\multilang@noend[1]{\cslet{end\@currenvir}{\relax}}
%    \end{macrocode}
% \end{macro}
%
%\iffalse
%</package>
%<*pkgtags>
%\fi
%
% \section{Implementation of Tags}
%
% \begin{macro}{\SetTagFilter}
% The |\SetTagFilter|\oarg{default}\marg{policy} sets the tag filter policy
% based on accept/deny rules in \meta{policy}.
%    \begin{macrocode}
\newcommand\SetTagFilter[2][accept]{%
  \kcvml@parsepolicy{kcvml@@tagfilter}{#1}{#2}}
\newcommand\kcvml@@tagfilter{}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\DefineTagFilter}
% The |\DefineTagFilter|\marg{name}\marg{default}\marg{policy} macro defines a
% tag filter policy under name \meta{name}.
%    \begin{macrocode}
\newcommand\DefineTagFilter[3]{%
  \kcvml@parsepolicy{kcvml@filter@@#1}{#2}{#3}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\UseFilter}
% The |\UseTagFilter|\marg{name} macro uses the previously defined tag filter
% policy with name \meta{name}.
%    \begin{macrocode}
\newcommand\UseTagFilter[1]{%
  \letcs\kcvml@@tagfilter{kcvml@filter@@#1}}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\kcvml@parsepolicy}
% The |\kcvml@parsepolicy|\marg{csname}\marg{default}\marg{policy}
% parses a tag filter policy, \meta{policy} with default \meta{default}, and
% stores the resulting filter in the control sequence \meta{csname}.
%    \begin{macrocode}
\newcommand\kcvml@parsepolicy[3]{%
%    \end{macrocode}
% We first reset the temporary filter variable |\kcvml@@tmptagfilter| then
% populate it via |\pgfqkeys|, first with the \meta{policy} list and
% subsequently with the \meta{default} policy.
%    \begin{macrocode}
  \bgroup
  \def\kcvml@@tmptagfilter{}%
  \pgfqkeys{kcvml/tagfilter}{#3,default/#2}%
%    \end{macrocode}
% Now we export the temporary |\kcvml@@tmptagfilter| to outside the local group
% and into the control sequence \meta{csname}.
%    \begin{macrocode}
  \edef\do{\egroup
    \unexpanded{\csdef{#1}}{\expandonce{\kcvml@@tmptagfilter}}}%
  \do}
%    \end{macrocode}
% The following lines specify how |\kcvml@@tmptagfilter| is modified when
% |accept| or |deny| filter rules are specified.
%    \begin{macrocode}
\pgfqkeys{kcvml/tagfilter}{%
  accept/.code={\kcvml@appendrule{#1}{\boolfalse}{\booltrue}},
  deny/.code  ={\kcvml@appendrule{#1}{\booltrue}{\boolfalse}},
  default/accept/.code n args={0}{\appto\kcvml@@tmptagfilter{%
    \kcvml@applydefault{\boolfalse}}},
  default/deny/.code n args={0}{\appto\kcvml@@tmptagfilter{%
    \kcvml@applydefault{\booltrue}}},
}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\kcvml@appendrule}
% The |\kcvml@appendrule|\marg{ruletags}\marg{flagmacro}\marg{invmacro} macro
% appends a filter rule to the overall tag filter. The rule filters for the
% given comma-separated list \meta{ruletags}.
% The \meta{flagmacro} specifies whether a match shall be disabled (if
% |\booltrue|) or enabled (if |\boolfalse|).
% The \meta{invmacro} must be the inverse of \meta{flagmacro}.
%    \begin{macrocode}
\newcommand\kcvml@appendrule[3]{%
  \bgroup
%    \end{macrocode}
% For simplified later processing, we turn \meta{ruletags} into an
% \textsf{etoolbox} list (in |\kcvml@@ruletags|) first.
%    \begin{macrocode}
  \def\kcvml@@ruletags{}%
  \forcsvlist{\listadd{\kcvml@@ruletags}}{#1}%
%    \end{macrocode}
% Now we append to the overall filter (in |\kcvml@@tmptagfilter|) outside the
% local group and use the cascade of |\expandafter|s to get |\cvmkl@@ruletags|
% out of the group without polluting the outer scope.
%    \begin{macrocode}
  \expandafter\egroup
  \expandafter\listadd\expandafter\kcvml@@tmptagfilter\expandafter{%
    \expandafter\kcvml@applyrule\expandafter{\kcvml@@ruletags}{#2}{#3}}}
%    \end{macrocode}
% \end{macro}
%
% We add the additional |tags| key to every disablable multilingual macro and
% environment. For this, we use \textsf{multilang}'s
% |\multilang@hook@processargs| hook.
%    \begin{macrocode}
\appto\multilang@hook@processargs{%
  \ifbool{multilang@@disablable}%
    {\eappto{\multilang@@keys}{%
%    \end{macrocode}
% Note that in |\multilang@@cekey|, the parent key of the command or environment
% is stored. Whenever the |tags| argument is used, we make it invoke
% |\kcvml@applyfilter| with the given \meta{tags} (|##1|).
%    \begin{macrocode}
      \noexpand\pgfqkeys{\multilang@@cekey}{%
        tags/.code={\noexpand\kcvml@applyfilter{##1}}}}}
    {}}
%    \end{macrocode}
%
% \begin{macro}{\kcvml@applyfilter}
% The |\kcvml@applyfilter|\marg{tags} macro applies the current filter, which is
% in the |\kcvml@@tagfilter| \textsf{etoolbox} list, to the comma-separated list
% \meta{tags} of tags to check whether the entity with the \meta{tags} should be
% disabled or not. The result of the check is stored in the Boolean flag
% |multilang@cmd@@disabled| for further use in with \textsf{multilang} code.
%    \begin{macrocode}
\newcommand\kcvml@applyfilter[1]{%
  \ifbool{multilang@cmd@@disabled}{}{%
%    \end{macrocode}
% We check the filter only if the entry has not already explicitly been marked
% as disabled. I.e., explicit disabling takes precedence, no matter whether it
% is specified before or after a |tags| element.
% In the Boolean flag |kcvml@@match|, we store whether a tag in \meta{tags}
% matched one of the accept/deny filters already. After initializing this flag,
% we iterate through |\kcvml@@tagfilter| with |\do|\marg{rule}, and
% we stop iterating after a match has been found.
%    \begin{macrocode}
  \boolfalse{kcvml@@match}%
  \def\do##1{%
%    \end{macrocode}
% Note that \meta{rule} is a curried macro whose missing last argument,
% \meta{tags}, is added here.
%    \begin{macrocode}
    ##1{#1}%
    \ifbool{kcvml@@match}{\listbreak}{}}%
  \dolistloop{\kcvml@@tagfilter}}}
\newbool{kcvml@@match}
%    \end{macrocode}
% \end{macro}
%
% \begin{macro}{\kcvml@applyrule}
% The
% |\kcvml@applyrule|\marg{ruletags}\marg{flagmacro}\marg{invmacro}\marg{tags}
% macro applies a single filter rule to the given \meta{tags}.
% The \meta{flagmacro} must be either |\booltrue| or |\boolfalse|.
% If it is |\booltrue|, this specifies that a match of \meta{tags} against
% \meta{ruletags} disables the display of the respective entity;
% If it is |\boolfalse|, this specifies that a match enables the display.
% The \meta{invmacro} must be the inverse of \meta{flagmacro}.
% We just check each tag in \meta{tags} individually.
%    \begin{macrocode}
\newcommand\kcvml@applyrule[4]{%
  \forcsvlist{\kcvml@applyrule@i{#1}{#2}{#3}}{#4}}
%    \end{macrocode}
%
% \begin{macro}{\kcvml@applyrule@i}
% The
% |\kcvml@applyrule@i|\marg{ruletags}\marg{flagmacro}\marg{invmacro}\marg{tag}
% macro applies a single filter rule to the given \meta{tag}.
% It checks whether the \meta{tag} is inverted (i.e., starting with ``|!|'') and
% hands over the actual check to |\kcvml@applyrule@ii|.
%    \begin{macrocode}
\newcommand\kcvml@applyrule@i[4]{%
  \if !\@car#4\@nil
    \expandafter\kcvml@applyrule@ii\expandafter{\@cdr#4\@nil}{#1}{#3}%
  \else
    \kcvml@applyrule@ii{#4}{#1}{#2}\fi}
%    \end{macrocode}
% \begin{macro}{\kcvml@applyrule@ii}
% The
% |\kcvml@applyrule@ii|\marg{tag}\marg{ruletags}\marg{flagmacro}
% macro applies a single filter rule to the given \meta{tag}.
% We check whether \meta{tag} in in the \textsf{etoolbox} list \meta{ruletags}.
% Since |\ifinlist| expects a list macro for its second argument (which it then
% expands once), we just give it |\empty| to eat (expand) and then use
% \meta{ruletags} as it is.
%    \begin{macrocode}
\newcommand\kcvml@applyrule@ii[3]{%
  \ifinlist{#1}{\empty #2}%
%    \end{macrocode}
% If we have a match, we apply \meta{flagmacro} to |multilang@cmd@@disabled| and
% then record, in |kcvml@@match|, that we found a match.
%    \begin{macrocode}
    {#3{multilang@cmd@@disabled}\booltrue{kcvml@@match}}{}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
%
% \begin{macro}{\kcvml@applydefault}
% The |\kcvml@applydefault|\marg{flagmacro}\marg{tags} macro applies a default
% filter to \meta{tags}. A \meta{flagmacro} of |\booltrue| corresponds to a
% ``default deny''; |\boolfalse| corresponds to ``default accept''.
%    \begin{macrocode}
\newcommand\kcvml@applydefault[2]{%
  #1{multilang@cmd@@disabled}}
%    \end{macrocode}
% \end{macro}
%
%\iffalse
%</pkgtags>
%<*pkgsect>
%\fi
%
% \section{Implementation of Sectioning Environments}
%
% The sectioning environments are proxies for the corresponding sectioning
% macros. They are defined as environments such that the whole environments
% rather than just the headings can be disabled.
% Each of the environments has one optional argument, |short| (for a short
% title), and one mandatory argument, |title| (for the actual title).
%
% \begin{environment}{Section}
% \begin{environment}{Section*}
% The |Section| and |Section*| environments are
% multilingual proxies to |\section| and, respectively, |\section*|.
%    \begin{macrocode}
\NewMultilangEnv{Section}{disablable,
  environment=section, oargs=short, margs=title}
\NewMultilangEnv{Section*}{disablable,
  environment=multilang@secstar, oargs=short, margs=title}
\newenvironment{multilang@secstar}{\section*}{}
%    \end{macrocode}
% \end{environment}
% \end{environment}
%
% \begin{environment}{SubSection}
% \begin{environment}{SubSection*}
% The |SubSection| and |SubSection*| environments are
% multilingual proxies to |\subsection| and, respectively, |\subsection*|.
%    \begin{macrocode}
\NewMultilangEnv{SubSection}{disablable,
  environment=subsection, oargs=short, margs=title}
\NewMultilangEnv{SubSection*}{disablable,
  environment=multilang@ssecstar, oargs=short, margs=title}
\newenvironment{multilang@ssecstar}{\subsection*}{}
%    \end{macrocode}
% \end{environment}
% \end{environment}
%
% \begin{environment}{SubSubSection}
% \begin{environment}{SubSubSection*}
% The |SubSubSection| and |SubSubSection*| environments are
% multilingual proxies to |\subsubsection| and, respectively, |\subsubsection*|.
%    \begin{macrocode}
\NewMultilangEnv{SubSubSection}{disablable,
  environment=subsubsection, oargs=short, margs=title}
\NewMultilangEnv{SubSubSection*}{disablable,
  environment=multilang@sssecstar, oargs=short, margs=title}
\newenvironment{multilang@sssecstar}{\subsubsection*}{}
%    \end{macrocode}
% \end{environment}
% \end{environment}
%
% \begin{environment}{Paragraph}
% \begin{environment}{Paragraph*}
% The |Paragraph| and |Paragraph*| environments are
% multilingual proxies to |\paragraph| and, respectively, |\paragraph*|.
%    \begin{macrocode}
\NewMultilangEnv{Paragraph}{disablable,
  environment=paragraph, oargs=short, margs=title}
\NewMultilangEnv{Paragraph*}{disablable,
  environment=multilang@parstar, oargs=short, margs=title}
\newenvironment{multilang@parstar}{\paragraph*}{}
%    \end{macrocode}
% \end{environment}
% \end{environment}
%
% \begin{environment}{SubParagraph}
% \begin{environment}{SubParagraph*}
% The |SubParagraph| and |SubParagraph*| environments are
% multilingual proxies to |\subparagraph| and, respectively, |\subparagraph*|.
%    \begin{macrocode}
\NewMultilangEnv{SubParagraph}{disablable,
  environment=subparagraph, oargs=short, margs=title}
\NewMultilangEnv{SubParagraph*}{disablable,
  environment=multilang@sparstar, oargs=short, margs=title}
\newenvironment{multilang@sparstar}{\subparagraph*}{}
%    \end{macrocode}
% \end{environment}
% \end{environment}
%
%
%\iffalse
%</pkgsect>
%\fi
% \Finale
\endinput