/****************************************************************************

**

** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).

** All rights reserved.

** Contact: Nokia Corporation (qt-info@nokia.com)

**

** This file is part of the documentation of the Qt Toolkit.

**

** $QT_BEGIN_LICENSE:LGPL$

** No Commercial Usage

** This file contains pre-release code and may not be distributed.

** You may use this file in accordance with the terms and conditions

** contained in the Technology Preview License Agreement accompanying

** this package.

**

** GNU Lesser General Public License Usage

** Alternatively, this file may be used under the terms of the GNU Lesser

** General Public License version 2.1 as published by the Free Software

** Foundation and appearing in the file LICENSE.LGPL included in the

** packaging of this file.  Please review the following information to

** ensure the GNU Lesser General Public License version 2.1 requirements

** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.

**

** In addition, as a special exception, Nokia gives you certain additional

** rights.  These rights are described in the Nokia Qt LGPL Exception

** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.

**

** If you have questions regarding the use of this file, please contact

** Nokia at qt-info@nokia.com.

**

**

**

**

**

**

**

**

** $QT_END_LICENSE$

**

****************************************************************************/

/*!

    \group i18n

    \title Qt Classes for Internationalization

    See \l{Internationalization with Qt} for information on how to use these classes

    in your applications.

*/

/*!

    \page internationalization.html

    \title Internationalization with Qt

    \brief Information about Qt's support for internationalization and multiple languages.

    \keyword internationalization

    \keyword i18n

    The internationalization of an application is the process of making

    the application usable by people in countries other than one's own.

    \tableofcontents

    \section1 Relevant Qt Classes and APIs

    These classes support internationalizing of Qt applications.

    \annotatedlist i18n

    \section1 Languages and Writing Systems

    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.

    Qt tries to make internationalization as painless as possible for

    developers. All input widgets and text drawing methods in Qt offer

    built-in support for all supported languages. The built-in font engine

    is capable of correctly and attractively rendering text that contains

    characters from a variety of different writing systems at the same

    time.

    Qt supports most languages in use today, in particular:

    \list

    \o All East Asian languages (Chinese, Japanese and Korean)

    \o All Western languages (using Latin script)

    \o Arabic

    \o Cyrillic languages (Russian, Ukrainian, etc.)

    \o Greek

    \o Hebrew

    \o Thai and Lao

    \o All scripts in Unicode 4.0 that do not require special processing

    \endlist

    On Windows, Unix/X11 with FontConfig (client side font support)

    and Qt for Embedded Linux the following languages are also supported:

    \list

    \o Bengali

    \o Devanagari

    \o Dhivehi (Thaana)

    \o Gujarati

    \o Gurmukhi

    \o Kannada

    \o Khmer

    \o Malayalam

    \o Myanmar

    \o Syriac

    \o Tamil

    \o Telugu

    \o Tibetan

    \endlist

    Many of these writing systems exhibit special features:

    \list

    \o \bold{Special line breaking behavior.} Some of the Asian languages are

    written without spaces between words. Line breaking can occur either

    after every character (with exceptions) as in Chinese, Japanese and

    Korean, or after logical word boundaries as in Thai.

    \o \bold{Bidirectional writing.} Arabic and Hebrew are written from right to

    left, except for numbers and embedded English text which is written

    left to right. The exact behavior is defined in the

    \l{http://www.unicode.org/unicode/reports/tr9/}{Unicode Technical Annex #9}.

    \o \bold{Non-spacing or diacritical marks (accents or umlauts in European

    languages).} Some languages such as Vietnamese make extensive use of

    these marks and some characters can have more than one mark at the

    same time to clarify pronunciation.

    \o \bold{Ligatures.} In special contexts, some pairs of characters get

    replaced by a combined glyph forming a ligature. Common examples are

    the fl and fi ligatures used in typesetting US and European books.

    \endlist

    Qt tries to take care of all the special features listed above. You

    usually don't have to worry about these features so long as you use

    Qt's input widgets (e.g. QLineEdit, QTextEdit, and derived classes)

    and Qt's display widgets (e.g. QLabel).

    Support for these writing systems is transparent to the

    programmer and completely encapsulated in \l{rich text

    processing}{Qt's text engine}. This means that you don't need to

    have any knowledge about the writing system used in a particular

    language, except for the following small points:

    \list

    \o QPainter::drawText(int x, int y, const QString &str) will always

    draw the string with its left edge at the position specified with

    the x, y parameters. This will usually give you left aligned strings.

    Arabic and Hebrew application strings are usually right

    aligned, so for these languages use the version of drawText() that

    takes a QRect since this will align in accordance with the language.

    \o When you write your own text input controls, use QTextLayout.

    In some languages (e.g. Arabic or languages from the Indian

    subcontinent), the width and shape of a glyph changes depending on the

    surrounding characters, which QTextLayout takes into account.

    Writing input controls usually requires a certain knowledge of the

    scripts it is going to be used in. Usually the easiest way is to

    subclass QLineEdit or QTextEdit.

    \endlist

    The following sections give some information on the status of the

    internationalization (i18n) support in Qt. See also the \l{Qt

    Linguist 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 4.0 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 \c{char *} to QString conversion overhead.

    Strings that are in "programmer space" (such as QObject names

    and file format texts) need not use QString; the traditional

    \c{char *} or the QByteArray class will suffice.

    You're unlikely to notice that you are using Unicode;

    QString, and QChar are just like easier versions of the crude

    \c{const char *} and char from traditional C.

    \section2 Use tr() for All Literal Text

    Wherever your program uses "quoted text" for text that will

    be presented to the user, ensure that it is processed by the \l

    QCoreApplication::translate() function. Essentially all that is necessary

    to achieve this is to use QObject::tr(). For example, assuming the

    \c LoginWidget is a subclass of QWidget:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 0

    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 QCoreApplication::translate() function

    directly:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 1

    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 \c lupdate utility described below.

    The macros expand to just the text (without the context).

    Example of QT_TR_NOOP():

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 2

    Example of QT_TRANSLATE_NOOP():

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 3

    If you disable the \c{const char *} to QString automatic

    conversion by compiling your software with the macro \c

    QT_NO_CAST_FROM_ASCII defined, you'll be very likely to catch any

    strings you are missing. See QString::fromLatin1() for more

    information. Disabling the conversion can make programming a bit

    cumbersome.

    If your source language uses characters outside Latin1, you

    might find QObject::trUtf8() more convenient than

    QObject::tr(), as tr() depends on the

    QTextCodec::codecForTr(), 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 Qt::CTRL + Qt::Key_Q for "quit" in your

    application, translators won't be able to override it. The

    correct idiom is

    \snippet examples/mainwindows/application/mainwindow.cpp 20

    \section2 Use QString::arg() for Dynamic Text

    The QString::arg() functions offer a simple means for substituting

    arguments:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 4

    In some languages the order of arguments may need to change, and this

    can easily be achieved by changing the order of the % arguments. For

    example:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 5

    produces the correct output in English and Norwegian:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 6

    \section2 Produce Translations

    Once you are using tr() throughout an application, you can start

    producing translations of the user-visible text in your program.

    The \l{Qt Linguist manual} provides further information about

    Qt's translation tools, \e{Qt Linguist}, \c lupdate and \c

    lrelease.

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

    \list 1

    \o Run \c 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 \c{QT_TR*_NOOP()} macros described above and

    produces TS files (usually one per language).

    \o Provide translations for the source texts in the TS file, using

    \e{Qt Linguist}. Since TS files are in XML format, you can also

    edit them by hand.

    \o Run \c lrelease to obtain a light-weight message file (a QM

    file) from the TS file, suitable only for end use. Think of the TS

    files as "source files", and QM files 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 \c lupdate utility does its best to reuse the

    translations from previous releases.

    Before you run \c lupdate, you should prepare a project file. Here's

    an example project file (\c .pro file):

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 7

    When you run \c lupdate or \c 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 \l{qmake}, you usually

    don't need an extra project file for \c lupdate; your \c qmake

    project file will work fine once you add the \c TRANSLATIONS

    entry.

    In your application, you must \l QTranslator::load() the translation

    files appropriate for the user's language, and install them using \l

    QCoreApplication::installTranslator().

    \c linguist, \c lupdate and \c lrelease are installed in the \c bin

    subdirectory of the base directory Qt is installed into. Click Help|Manual

    in \e{Qt Linguist} to access the user's manual; it contains a tutorial

    to get you started.

    \target qt-itself

    Qt itself contains over 400 strings that will also need to be

    translated into the languages that you are targeting. You will find

    translation files for French, German and Simplified Chinese in

    \c{$QTDIR/translations}, as well as a template for translating to

    other languages. (This directory also contains some additional

    unsupported translations which may be useful.)

    Typically, your application's \c main() function will look like

    this:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 8

    Note the use of QLibraryInfo::location() to locate the Qt translations.

    Developers should request the path to the translations at run-time by

    passing QLibraryInfo::TranslationsPath to this function instead of

    using the \c QTDIR environment variable in their applications.

    \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:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 9

    For converting Unicode to local 8-bit encodings, a shortcut is

    available: the QString::toLocal8Bit() function returns such 8-bit

    data. Another useful shortcut is QString::toUtf8(), which returns

    text in the 8-bit UTF-8 encoding: this perfectly preserves

    Unicode information while looking like plain ASCII if the text is

    wholly 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:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 10

    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 (UTF-16 or

    UTF-8) 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()).

    Qt supports most of the more frequently used encodings natively. For a

    complete list of supported encodings see the \l QTextCodec

    documentation.

    In some cases and for less frequently used encodings it may be

    necessary to write your own QTextCodec subclass. Depending on the

    urgency, it may be useful to contact Qt's technical support team or

    ask on the \c qt-interest mailing list to see if someone else is

    already working on supporting the encoding.

    \keyword localization

    \section2 Localize

    Localization is the process of adapting to local conventions, for

    example presenting dates and times using the locally preferred

    formats. Such localizations can be accomplished using appropriate tr()

    strings.

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 11

    In the example, for the US we would leave the translation of

    "AMPM" as it is and thereby use the 12-hour clock branch; but in

    Europe we would translate it as something else and this will make

    the code use the 24-hour clock branch.

    For localized numbers use the QLocale class.

    Localizing images is not recommended. Choose clear icons that are

    appropriate for all localities, rather than relying on local puns or

    stretched metaphors. The exception is for images of left and right

    pointing arrows which may need to be reversed for Arabic and Hebrew

    locales.

    \section1 Dynamic Translation

    Some applications, such as Qt Linguist, must be able to support changes

    to the user's language settings while they are still running. To make

    widgets aware of changes to the installed QTranslators, reimplement the 

    widget's \l{QWidget::changeEvent()}{changeEvent()} function to check whether 

    the event is a \l{QEvent::LanguageChange}{LanguageChange} event, and update

    the text displayed by widgets using the \l{QObject::tr()}{tr()} function

    in the usual way. For example:

    \snippet doc/src/snippets/code/doc_src_i18n.qdoc 12

    All other change events should be passed on by calling the default

    implementation of the function.

    The list of installed translators might change in reaction to a 

    \l{QEvent::LocaleChange}{LocaleChange} event, or the application might

    provide a user interface that allows the user to change the current

    application language.

    The default event handler for QWidget subclasses responds to the

    QEvent::LanguageChange event, and will call this function when necessary;

    other application components can also force widgets to update themselves

    by posting the \l{QEvent::LanguageChange}{LanguageChange} event to them.

    \section1 Translating Non-Qt Classes

    It is sometimes necessary to provide internationalization support for

    strings used in classes that do not inherit QObject or use the Q_OBJECT

    macro to enable translation features. Since Qt translates strings at

    run-time based on the class they are associated with and \c lupdate

    looks for translatable strings in the source code, non-Qt classes must

    use mechanisms that also provide this information.

    One way to do this is to add translation support to a non-Qt class

    using the Q_DECLARE_TR_FUNCTIONS() macro; for example:

    \snippet doc/src/snippets/i18n-non-qt-class/myclass.h 0

    \dots

    \snippet doc/src/snippets/i18n-non-qt-class/myclass.h 1

    This provides the class with \l{QObject::}{tr()} functions that can

    be used to translate strings associated with the class, and makes it

    possible for \c lupdate to find translatable strings in the source

    code.

    Alternatively, the QCoreApplication::translate() function can be called

    with a specific context, and this will be recognized by \c lupdate and

    Qt Linguist.

    \section1 System Support

    Some of the operating systems and windowing systems that Qt runs on

    only have limited support for Unicode. The level of support available

    in the underlying system has some influence on the support that Qt can

    provide on those platforms, although in general Qt applications need

    not be too concerned with platform-specific limitations.

    \section2 Unix/X11

    \list

    \o  Locale-oriented fonts and input methods. Qt hides these and

        provides Unicode input and output.

    \o  Filesystem conventions such as

        \l{http://www.ietf.org/rfc/rfc2279.txt}{UTF-8}

        are under development in some Unix variants. All Qt file

        functions allow Unicode, but convert filenames to the local

        8-bit encoding, as this is the Unix convention (see

        QFile::setEncodingFunction() to explore alternative

        encodings).

    \o  File I/O defaults to the local 8-bit encoding,

        with Unicode options in QTextStream.

    \o  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 the

        \c /usr/share/locale/ja_JP.EUC directory needs to be complete. For

        best results, use complete locales from your system vendor.

    \endlist

    \section2 Windows

    \list

    \o  Qt provides full Unicode support, including input methods, fonts,

        clipboard, drag-and-drop and file names.

    \o  File I/O defaults to Latin1, 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.

    \o  Unlike programs written with MFC or plain winlib, Qt programs

        are portable between Windows 98 and Windows NT.

        \e {You do not need different binaries to support Unicode.}

    \endlist

    \section2 Mac OS X

    For details on Mac-specific translation, refer to the Qt/Mac Specific Issues

    document \l{Qt for Mac OS X - Specific Issues#Translating the Application Menu and Native Dialogs}{here}.

*/