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<div class="chapter">
<div class="titlepage"><div><div><h1 class="title">
<a name="chapter-internationalization"></a>Chapter 27. Internationalization and Localization</h1></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<ul class="toc">
<li><span class="section"><a href="chapter-internationalization.html#sec-internationalization-intro">Preparing your project</a></span></li>
<li><span class="section"><a href="sec-i18n-marking-strings.html">Marking strings for translation</a></span></li>
<li><span class="section"><a href="sec-i18n-expecting-utf8.html">Expecting UTF8</a></span></li>
<li><span class="section"><a href="sec-i18n-pitfalls.html">Pitfalls</a></span></li>
<li><span class="section"><a href="sec-i18n-getting-help-with-translations.html">Getting help with translations</a></span></li>
</ul>
</div>
<p>
<span class="application">gtkmm</span> applications can easily support multiple languages, including
non-European languages such as Chinese and right-to-left languages such as
Arabic. An appropriately-written and translated <span class="application">gtkmm</span> application will use
the appropriate language at runtime based on the user's environment.
</p>
<p>
You might not anticipate the need to support additional languages, but
you can never rule it out. And it's easier to develop the application
properly in the first place rather than retrofitting later.
</p>
<p>
The process of writing source code that allows for translation is called
<code class="literal">internationalization</code>, often abbreviated to
<code class="literal">i18n</code>. The <code class="literal">Localization</code> process,
sometimes abbreviated as <code class="literal">l10n</code>, provides translated text
for other languages, based on that source code.
</p>
<p>
The main activity in the internationalization process is finding strings
seen by users and marking them for translation. You do not need to do it all
at once - if you set up the necessary project infrastructure correctly then
your application will work normally regardless of how many strings you've
covered.
</p>
<p>
String literals should be typed in the source code in English, but
surrounded by a macro. The <span class="application">gettext</span> (or intltool)
utility can then extract the marked strings for translation, and substitute
the translated text at runtime.
</p>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sec-internationalization-intro"></a>Preparing your project</h2></div></div></div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="icons/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top">
<p>
In the instructions below we will assume that you will not be using
<span class="application">gettext</span> directly, but
<span class="application">intltool</span>, which was written specifically for
<code class="literal">GNOME</code>. <span class="application">intltool</span> uses
<code class="function">gettext()</code>, which extracts strings from source code,
but <span class="application">intltool</span> can also combine strings from
other files, for example from desktop menu details, and GUI resource
files such as <code class="filename">.ui</code> files, into standard
<span class="application">gettext</span> <code class="filename">.pot/.po</code> files.
</p>
<p>
We also assume that you are using autotools (<span class="application">automake</span>
and <span class="application">autoconf</span>) to build your project (although
autotools is not recommended for new applications), and
that you are using <a class="ulink" href="https://gitlab.gnome.org/GNOME/gnome-common/blob/master/autogen.sh" target="_top">
<code class="literal">./autogen.sh</code> from <span class="application">gnome-common</span></a>
or a similar <code class="literal">autogen.sh</code> file, which, among other
things, takes care of some <span class="application">intltool</span>
initialization.
</p>
</td></tr>
</table></div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="icons/note.png"></td>
<th align="left">Note</th>
</tr>
<tr><td align="left" valign="top">
<p>
If you are using <span class="application">meson</span> (recommended), see the
<a class="ulink" href="https://mesonbuild.com/Localisation.html" target="_top">Localisation</a>
chapter in Meson's manual. You can then skip this section.
</p>
</td></tr>
</table></div>
<p>
An alternative to <span class="application">gnome-common</span>'s
<code class="literal">autogen.sh</code> may look like this:
</p>
<pre class="programlisting"><code class="code">#! /bin/sh -e
test -n "$srcdir" || srcdir=`dirname "$0"`
test -n "$srcdir" || srcdir=.
autoreconf --force --install --verbose --warnings=all "$srcdir"
echo "Running intltoolize --copy --force --automake"
intltoolize --copy --force --automake
test -n "$NOCONFIGURE" || "$srcdir/configure" "$@"</code></pre>
<p>
Create a sub-directory named <code class="literal">po</code> in your project's root
directory. This directory will eventually contain all of your
translations. Within it, create a file named <code class="literal">LINGUAS</code>
and a file named <code class="literal">POTFILES.in</code>. It is common practice to
also create a <code class="literal">ChangeLog</code> file in the
<code class="literal">po</code> directory so that translators can keep track of
translation changes.
</p>
<p>
<code class="literal">LINGUAS</code> contains an alphabetically sorted list of codes
identifying the languages for which your program is translated (comment
lines starting with a <code class="literal">#</code> are ignored). Each language
code listed in the <code class="literal">LINGUAS</code> file must have a
corresponding <code class="literal">.po</code> file. So, if your program has German
and Japanese translations, your <code class="literal">LINGUAS</code> file would
look like this:
</p>
<pre class="programlisting"><code class="code"># keep this file sorted alphabetically, one language code per line
de
ja</code></pre>
<p>
(In addition, you'd have the files <code class="literal">de.po</code> and
<code class="literal">ja.po</code> in your
<code class="literal">po</code> directory which contain the German and Japanese
translations, respectively.)
</p>
<p>
<code class="literal">POTFILES.in</code> is a list of paths to all files which
contain strings marked up for translation, starting from the project root
directory. So for example, if your project sources were located in a
subdirectory named <code class="literal">src</code>, and you had two files that
contained strings that should be translated, your
<code class="literal">POTFILES.in</code> file might look like this:
</p>
<pre class="programlisting"><code class="code">src/main.cc
src/other.cc</code></pre>
<p>
If you are using <span class="application">gettext</span> directly, you can only
mark strings for translation if they are in source code file. However, if
you use <span class="application">intltool</span>, you can mark strings for
translation in a variety of other file formats, including
<code class="filename">.ui</code> files, xml,
<a class="ulink" href="http://standards.freedesktop.org/desktop-entry-spec/latest/" target="_top">.desktop files</a>
and several more. So, if you have designed some of the
application UI in xml files then also add your
<code class="filename">.ui</code> files to the list in
<code class="literal">POTFILES.in</code>.
</p>
<p>
Now that there is a place to put your translations, you need to initialize
<span class="application">intltool</span> and <span class="application">gettext</span>.
Add the following code to your <code class="literal">configure.ac</code>,
substituting 'programname' with the name of your program:
</p>
<pre class="programlisting"><code class="code">IT_PROG_INTLTOOL([0.35.0])
GETTEXT_PACKAGE=programname
AC_SUBST(GETTEXT_PACKAGE)
AC_DEFINE_UNQUOTED([GETTEXT_PACKAGE], ["$GETTEXT_PACKAGE"],
[The domain to use with gettext])
AM_GNU_GETTEXT([external])
AM_GNU_GETTEXT_VERSION([0.17])
PROGRAMNAME_LOCALEDIR=[${datadir}/locale]
AC_SUBST(PROGRAMNAME_LOCALEDIR)</code></pre>
<p>
This <code class="varname">PROGRAMNAME_LOCALEDIR</code> variable will be used later
in the <code class="literal">Makefile.am</code> file, to define a macro that will be
used when you initialize <span class="application">gettext</span> in your source
code.
</p>
<p>
<code class="literal">AM_GLIB_GNU_GETTEXT</code> has been an alternative to
<code class="literal">AM_GNU_GETTEXT</code> and <code class="literal">AM_GNU_GETTEXT_VERSION</code>,
but <code class="literal">AM_GLIB_GNU_GETTEXT</code> is now deprecated, and shall
not be used in new code.
</p>
<p>
In the top-level Makefile.am:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<p>Add <code class="literal">po</code> to the <code class="literal">SUBDIRS</code>
variable. Without this, your translations won't get built and
installed when you build the program</p>
</li>
<li class="listitem">
<p>
Define <code class="literal">INTLTOOL_FILES</code> as:</p>
<pre class="programlisting"><code class="code">INTLTOOL_FILES = intltool-extract.in \
intltool-merge.in \
intltool-update.in</code></pre>
</li>
<li class="listitem">
<p>
Add <code class="literal">INTLTOOL_FILES</code> to the
<code class="literal">EXTRA_DIST</code> list of files. This ensures that when
you do a <span class="command"><strong>make dist</strong></span>, these files will be
included in the source tarball.
</p>
</li>
<li class="listitem">
<p>
Update your <code class="literal">DISTCLEANFILES</code>:</p>
<pre class="programlisting"><code class="code">DISTCLEANFILES = ... intltool-extract \
intltool-merge \
intltool-update \
po/.intltool-merge-cache</code></pre>
</li>
<li class="listitem">
<p>
Depending on the types of files that contain translatable strings,
add code such as</p>
<pre class="programlisting"><code class="code">desktopdir = $(datadir)/applications
desktop_in_files = programname.desktop.in
desktop_DATA = $(desktop_in_files:.desktop.in=.desktop)
@INTLTOOL_DESKTOP_RULE@</code></pre>
</li>
</ul></div>
<p>
</p>
<p>
In your <code class="literal">src/Makefile.am</code>, update your
<code class="literal">AM_CPPFLAGS</code> to add the following preprocessor macro
definition:
</p>
<pre class="programlisting"><code class="code">AM_CPPFLAGS = ... -DPROGRAMNAME_LOCALEDIR=\"${PROGRAMNAME_LOCALEDIR}\"</code></pre>
<p>
This macro will be used when you initialize <code class="literal">gettext</code> in
your source code.
</p>
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