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/*! \defgroup i18n

\title Internationalization with Qt

\keyword internationalization

The internationalization of an application is the process of making
the application usable by people in countries other than one's own. 

In some cases internationalization is simple, for example, making a US
application accessible to Australian or British users may require
little more than a few spelling corrections. But to make a US
application usable by Japanese users, or a Korean application usable
by German users, will require that the software operate not only in
different languages, but use different input techniques, character
encodings and presentation conventions.

See also the \link linguist-manual.book Qt Linguist\endlink manual.

\section1 Step by Step

Writing cross-platform international software with Qt is a gentle,
incremental process. Your software can become internationalized in
the following stages:

\section2 Use QString for all User-visible Text

Since QString uses the Unicode encoding internally, every
language in the world can be processed transparently using
familiar text processing operations. Also, since all Qt
functions that present text to the user take a QString as a
parameter, there is no char* to QString conversion time overhead.

Strings that are in "programmer space" (such as QObject names
and file format texts) need not use QString; the traditional
char* or the QCString class will suffice.

You're unlikely to notice that you are using Unicode;
QString, and QChar are just like easier versions of the crude
const char* and char from traditional C.

\section2 Use \link QObject::tr() tr()\endlink for all Literal Text

Wherever your program uses \c {"quoted text"} for text that will
be presented to the user, ensure that it is processed by the \l
QApplication::translate() function. Essentially all that is necessary
to achieve this is to use \l QObject::tr(). For example, assuming
\c LoginWidget is a subclass of QWidget:

\code
    LoginWidget::LoginWidget()
    {
	QLabel *label = new QLabel( tr("Password:"), this );
	...
    }
\endcode

This accounts for 99% of the user-visible strings you're likely to
write.

If the quoted text is not in a member function of a
QObject subclass, use either the tr() function of an
appropriate class, or the QApplication::translate() function
directly:

\code
    void some_global_function( LoginWidget *logwid )
    {
	QLabel *label = new QLabel(
		LoginWidget::tr("Password:"), logwid );
    }

    void same_global_function( LoginWidget *logwid )
    {
	QLabel *label = new QLabel(
		qApp->translate("LoginWidget", "Password:"),
		logwid );
    }
\endcode

If you need to have translatable text completely
outside a function, there are two macros to help: QT_TR_NOOP()
and QT_TRANSLATE_NOOP(). They merely mark the text for
extraction by the \e lupdate utility described below.
The macros expand to just the text (without the context).

Example of QT_TR_NOOP():
\code
    QString FriendlyConversation::greeting( int greet_type )
    {
	static const char* greeting_strings[] = {
	    QT_TR_NOOP( "Hello" ),
	    QT_TR_NOOP( "Goodbye" )
	};
	return tr( greeting_strings[greet_type] );
    }
\endcode

Example of QT_TRANSLATE_NOOP():
\code
    static const char* greeting_strings[] = {
	QT_TRANSLATE_NOOP( "FriendlyConversation", "Hello" ),
	QT_TRANSLATE_NOOP( "FriendlyConversation", "Goodbye" )
    };

    QString FriendlyConversation::greeting( int greet_type )
    {
	return tr( greeting_strings[greet_type] );
    }

    QString global_greeting( int greet_type )
    {
	return qApp->translate( "FriendlyConversation",
				greeting_strings[greet_type] );
    }
\endcode

If you disable the const char* to QString automatic conversion
by compiling your software with the macro QT_NO_CAST_ASCII
defined, you'll be very likely to catch any strings you are
missing. See QString::fromLatin1() for more information.
Disabling the conversion makes programming cumbersome.

If your source language uses characters outside Latin-1, you
might find QObject::trUtf8() more convenient than
QObject::tr(), as tr() depends on the
QApplication::defaultCodec(), which makes it more fragile than
QObject::trUtf8().

\section2 Use QKeySequence() for Accelerator Values

Accelerator values such as Ctrl+Q or Alt+F need to be
translated too. If you hardcode \c CTRL+Key_Q for "Quit" in
your application, translators won't be able to override
it. The correct idiom is

\code
    QPopupMenu *file = new QPopupMenu( this );
    file->insertItem( tr("&Quit"), this, SLOT(quit()),
		      QKeySequence(tr("Ctrl+Q", "File|Quit")) );
\endcode

\section2 Use QString::arg() for Simple Arguments

The printf() style of inserting arguments in strings
is often a poor choice for internationalized text, as it is
sometimes necessary to change the order of arguments when
translating. Nonetheless, the QString::arg()
functions offer a simple means for substituting arguments:
\code
    void FileCopier::showProgress( int done, int total,
				   const QString& current_file )
    {
	label.setText( tr("%1 of %2 files copied.\nCopying: %3")
			.arg(done)
			.arg(total)
			.arg(current_file) );
    }
\endcode

\section2 Produce Translations

Once you are using tr() throughout an application, you can start
producing translations of the user-visible text in your program.

\link linguist-manual.book Qt Linguist\endlink's manual provides
further information about Qt's translation tools, \e{Qt Linguist}, \e
lupdate and \e lrelease.

Translation of a Qt application is a three-step process:

\list 1
  \i Run \e lupdate to extract translatable text from
  the C++ source code of the Qt application, resulting in a
  message file for translators (a .ts file). The utility
  recognizes the tr() construct and the QT_*_NOOP macros described
  above and produces .ts files (usually one per language).
  \i Provide translations for the source texts in the .ts
  file, using Qt Linguist. Since .ts files are in XML
  format, you can also edit them by hand.
  \i Run \e lrelease to obtain a light-weight message
  file (a .qm file) from the .ts file, suitable only for end
  use. 	You can see the .ts files as "source files", and .qm
  as "object files". The translator edits the .ts files, but
  the users of your application only need the .qm files. Both
  kinds of files are platform and locale independent.
\endlist

Typically, you will repeat these steps for every release of
your application. The \e lupdate utility does its best
to reuse the translations from previous releases.

Before you run \e lupdate, you should prepare a project
file. Here's an example project file (.pro file):

\code
    HEADERS         = funnydialog.h \
		      wackywidget.h
    SOURCES         = funnydialog.cpp \
		      main.cpp \
		      wackywidget.cpp
    FORMS           = fancybox.ui
    TRANSLATIONS    = superapp_dk.ts \
		      superapp_fi.ts \
		      superapp_no.ts \
		      superapp_se.ts
\endcode

When you run \e lupdate or \e lrelease, you
must give the name of the project file as a command-line
argument.

In this example, four exotic languages are supported: Danish,
Finnish, Norwegian and Swedish. If you use qmake (or tmake), you
usually don't need an extra project file for \e lupdate; your
qmake project file will work fine once you add the TRANSLATIONS entry.

In your application, you must \l QTranslator::load()
the translation files appropriate for the user's language, and
install them using \l QApplication::installTranslator().

If you have been using the old Qt tools (findtr, msg2qm and
mergetr), you can use \e qm2ts to convert your old
.qm files.

\e linguist, \e lupdate and \e lrelease are installed in
\c $QTDIR/bin. Click Help|Manual in Qt Linguist to access the
user's manual; it contains a tutorial to get you started.

While these utilities offer a convenient way to create .qm files, any
system that writes .qm files is sufficient. You could make an
application that adds translations to a QTranslator with
QTranslator::insert() and then writes a .qm file with
QTranslator::save(). This way the translations can come from any
source you choose.

\target qt-itself
Qt itself contains about 400 strings that will also need to be
translated into the languages that you are targeting. You will find
translation files for French and German in \c $QTDIR/translations
as well as a template for translating to other languages.

Typically, your application's main() function will look like this:
\code
    int main( int argc, char **argv )
    {
	QApplication app( argc, argv );

	// translation file for Qt
	QTranslator qt( 0 );
	qt.load( QString( "qt_" ) + QTextCodec::locale(), "." );
	app.installTranslator( &qt );

	// translation file for application strings
	QTranslator myapp( 0 );
	myapp.load( QString( "myapp_" ) + QTextCodec::locale(), "." );
	app.installTranslator( &myapp );

	...

	return app.exec();
    }
\endcode

\section2 Support for Encodings

The QTextCodec class and the facilities in QTextStream make it easy
to support many input and output encodings for your users' data. When
an application starts, the locale of the machine will determine the
8-bit encoding used when dealing with 8-bit data - such as for font
selection, text display, 8-bit text I/O and character input.

The application may occasionally require encodings other
than the default local 8-bit encoding. For example, an application
in a Cyrillic KOI8-R locale (the de-facto standard locale in Russia)
might need to output Cyrillic in the ISO 8859-5 encoding. Code for
this would be:

\code
    QString string = ...; // some Unicode text

    QTextCodec* codec = QTextCodec::codecForName( "ISO 8859-5" );
    QCString encoded_string = codec->fromUnicode( string );

    ...; // use encoded_string in 8-bit operations
\endcode

For converting Unicode to local 8-bit encodings,
a shortcut is available: the
\link QString::local8Bit() local8Bit\endlink() method of
QString returns such 8-bit data. Another useful shortcut
is the \link QString::utf8() utf8\endlink() method, which
returns text in the 8-bit UTF-8 encoding - interesting in
that it perfectly preserves Unicode information while looking
like plain US-ASCII if the Unicode is wholly US-ASCII.

For converting the other way, there are the QString::fromUtf8() and
QString::fromLocal8Bit() convenience functions, or the general code,
demonstrated by this conversion from ISO 8859-5 Cyrillic to Unicode
conversion:

\code
    QCString encoded_string = ...; // Some ISO 8859-5 encoded text.

    QTextCodec* codec = QTextCodec::codecForName("ISO 8859-5");
    QString string = codec->toUnicode(encoded_string);

    ...; // Use string in all of Qt's QString operations.
\endcode

Ideally Unicode I/O should be used as this maximizes the portability
of documents between users around the world, but in reality it is
useful to support all the appropriate encodings that your users will
need to process existing documents. In general, Unicode (UTF16 or
UTF8) is best for information transferred between arbitrary
people, while within a language or national group, a local standard
is often more appropriate. The most important encoding to support is
the one returned by QTextCodec::codecForLocale(), as this is the one
the user is most likely to need for communicating with other people
and applications (this is the codec used by local8Bit()).

Since most Unix systems do not have built-in support for converting
between local 8-bit encodings and Unicode, it may be necessary to
write your own QTextCodec subclass. Depending on the urgency, it
may be useful to contact Trolltech technical support or ask on
the qt-interest mailing list to see if someone else is already working
on supporting the encoding. A useful interim measure can be to
use the QTextCodec::loadCharmapFile() function to build a data-driven
codec, although this approach has a memory and speed penalty,
especially with dynamically loaded libraries. For details of writing
your own QTextCodec, see the main QTextCodec class documentation.

\keyword localization

\section2 Localize

Localization is the process of adapting to local conventions
such as date and time presentations. Such localizations can be
accomplished using appropriate tr() strings, even "magic" words,
as this somewhat contrived example shows:

\code
    void Clock::setTime(const QTime& t)
    {
	if ( tr("AMPM") == "AMPM" ) {
	    // 12-hour clock
	} else {
	    // 24-hour clock
	}
    }
\endcode

Localizing images is not recommended. Choose clear icons that are
appropriate for all localities, rather than relying on local puns or
stretched metaphors.

\section1 System Support

Operating systems and window systems supporting Unicode are still in
the early stages of development. The level of support
available in the underlying system influences the support Qt provides
on that platform, but applications written with Qt need not generally
be too concerned with the actual limitations.

\section2 Unix/X11

\list
\i Locale-oriented fonts and input methods. Qt hides these and
    provides Unicode input and output.
\i Filesystem conventions such as
    \link http://www.ietf.org/rfc/rfc2279.txt UTF-8 \endlink
    are under development
    in some Unix variants. All Qt file functions allow Unicode,
    but convert all filenames to the local 8-bit encoding, as
    this is the Unix convention
    (see QFile::setEncodingFunction()
	to explore alternative encodings).
\i File I/O defaults to the local 8-bit encoding,
    with Unicode options in QTextStream.
\endlist

\section2 Windows 95/98/NT

\list
\i Qt provides full Unicode support, including input methods, fonts,
    clipboard, drag-and-drop and file names.
\i File I/O defaults to Latin-1, with Unicode options in QTextStream.
    Note that some Windows programs do not understand big-endian
    Unicode text files even though that is the order prescribed by
    the Unicode Standard in the absence of higher-level protocols.
\i Unlike programs written with MFC or plain winlib, Qt programs
    are portable between Windows 95/98 and Windows NT.
    \e {You do not need different binaries to support Unicode.}
\endlist

\section1 Supporting More Input Methods

While Trolltech doesn't have the resources or expertise in all the
languages of the world to immediately include support in Qt, we are
very keen to work with people who do have the expertise. Over the
next few minor version numbers, we hope to add support for your
language of choice, until everyone can use Qt and all the programs
developed with Qt, regardless of their language.

Languages with single-byte encodings
(European Latin-1 and KOI8-R, etc.) and multi-byte encodings 
(East Asian EUC-JP, etc.) are supported. 
Support for the "complex" encodings - those requiring
right-to-left input or complex character composition (eg. Arabic,
Hebrew, and Thai script) is implemented, but the range of Indic scripts
(Hindi, Devanagari, Bengali, etc.) is still under development. 
The current state of activity is:

\table
\header \i Encodings \i Status
\row 
\i All encodings on Windows
\i The local encoding is always supported.
\row
\i ISO standard encodings
	ISO 8859-1,
	ISO 8859-2,
	ISO 8859-3,
	ISO 8859-4,
	ISO 8859-5,
	ISO 8859-7,
	ISO 8859-9, and
	ISO 8859-15
\i Fully supported.
\row
\i KOI8-R
\i Fully supported.
\row
\i eucJP, JIS, and ShiftJIS
\i Fully supported. Uses eucJP with the XIM protocol on X11,
	and the IME Windows NT in Japanese Windows NT.
	Serika Kurusugawa and others are assisting with this effort.
	\link ftp://ftp.sra.co.jp/pub/x11/kinput2/ kinput2 \endlink
	is the tested input method for X11.
\row
\i eucKR
\i Supported.
	Mizi Research are assisting with this effort.
	\link http://www.mizi.com hanIM \endlink
       	is the tested input method.
\row
\i Big5
\i Qt contains a Big5 codec developed by Ming Che-Chuang.
	Testing is underway with the xcin (2.5.x) XIM server.
\row
\i eucTW
\i Under external development.
\endtable

More information on the support of different writing systems in Qt can be found
in \link scripts.html the documentation about writing systems \endlink.

If you are interested in contributing to existing efforts, or
supporting new encodings beyond those mentioned above, your
work can be considered for inclusion in the official Qt distribution,
or just included with your application.

Eventually, we hope to help Unix become as Unicode-oriented as
Windows is becoming. This means better font support in the font servers,
with new developments like the True Type font servers
\link http://www.dcs.ed.ac.uk/home/jec/programs/xfsft/ xfsft \endlink,
\link ftp://sunsite.unc.edu/pub/Linux/X11/fonts/ xfstt \endlink,
and x-tt, as well as
\link http://www.ietf.org/rfc/rfc2279.txt UTF-8 \endlink
(a Unicode encoding) filenames such as with the
\link http://www.sun.com/software/white-papers/wp-unicode/ Unicode
support in Solaris 7 \endlink.

\section1 Note about Locales on X11

Many Unix distributions contain only partial support for some locales.
For example, if you have a \c /usr/share/locale/ja_JP.EUC
directory, this does not necessarily mean you can display Japanese text;
you also need JIS encoded fonts (or Unicode fonts), and that
\c /usr/share/locale/ja_JP.EUC directory needs to be complete.
For best results, use complete locales from your system vendor.

\section1 Relevant Qt Classes

These classes are relevant to internationalizing Qt applications.
*/