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/*!
\group i18n
\brief How to internationalize your Qt application.
\title Qt Classes for Internationalization
See \l{Internationalization with Qt} for information on how to use these classes
in your applications.
*/
/*!
\group internationalization
\title Internationalization with Qt
\brief Information about Qt's support for internationalization and multiple languages.
\nextpage Writing Source Code for Translation
\keyword internationalization
\keyword i18n
The \e internationalization and \e localization of an application are the
processes of adapting the application to different languages, regional
differences and technical requirements of a target market.
Internationalization means designing a software application so that it can
be adapted to various languages and regions without engineering changes.
Localization means adapting internationalized software for a specific region
or language by adding locale-specific components (such as date, time, and
number formats) and translating text.
\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 controls 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
\li All East Asian languages (Chinese, Japanese and Korean)
\li All Western languages (using Latin script)
\li Arabic
\li Cyrillic languages (Russian, Ukrainian, etc.)
\li Greek
\li Hebrew
\li Thai and Lao
\li All scripts in Unicode 6.2 that do not require special processing
\li Bengali
\li Burmese (Myanmar)
\li Devanagari
\li Gujarati
\li Gurmukhi
\li Kannada
\li Khmer
\li Malayalam
\li Tamil
\li Telugu
\li Tibetan
\endlist
The list above is supported and will work on all platforms as long as
the system has fonts to render these writing systems installed.
On Windows, Linux and Unix with FontConfig (client side font support)
the following languages are also supported:
\list
\li Dhivehi (Thaana)
\li Syriac
\li N'Ko
\endlist
On \macos, the following languages are also supported:
\list
\li Oriya
\li Sinhala
\endlist
Many of these writing systems exhibit special features:
\list
\li \b{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.
\li \b{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}.
\li \b{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.
\li \b{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 controls (e.g. QLineEdit, QTextEdit, and derived classes
or the Quick TextInput item) and Qt's display controls (e.g. QLabel
and Qt Quick's Text item).
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 usually need to have any knowledge of the writing
system used in a particular language, unless you want to write your own text
input controls. In some languages, such as Arabic or languages from the
Indian subcontinent, the width and shape of a glyph changes depending on the
surrounding characters. To take this into account, use QTextLayout.
Writing input controls also requires some knowledge of the scripts they are
going to be used in. Usually, the easiest way is to subclass QLineEdit or
QTextEdit.
For more information about how to internationalize source code, see
\l{Writing Source Code for Translation} and
\l{Internationalization and Localization with Qt Quick}.
\section1 Producing Translations
Qt provides excellent support for translating Qt C++ and Qt Quick
applications into local languages. Release managers, translators, and
developers can use the Qt translation tools to accomplish their tasks.
The Qt translation tools, Qt Linguist, \c lupdate, and \c lrelease are
installed in the \c bin subdirectory of the base directory Qt is installed
into. For more information about using them, see the \l{Qt Linguist Manual}.
\target qt-itself
Qt itself contains several thousands of strings that will also need to be
translated into the languages that you are targeting. You will find
a number of translation files in the qttranslations repository.
Before you start translating Qt, read the wiki page
\l{external: Translating Qt Into Other Languages}
{Translating Qt Into Other Languages}.
\section1 Enabling Translation
Typically, your application's \c main() function will look like
this:
\snippet snippets/code/doc_src_i18n.cpp 8
For a translation-aware application, a QTranslator object is created, then a
translation is loaded according to the user's preferred UI display locale at
runtime, and finally, the translator object is installed into the
application.
\section1 Locating Qt Translations
You can also use QLibraryInfo::location() to locate the translations for the
Qt modules used. You can request the path to the translations at run-time by
passing QLibraryInfo::TranslationsPath to this function.
\section2 Available Catalogs
The Qt translation catalogs are located in the \c qttranslations repository.
\warning Qt translations are contributed by the Qt community, and provided
without any guarantees. Translations migh be missing, outdated, or entirely
incorrect, up to the point of being malicious. It is recommended that you
audit any translations you ship.
The \c qt_ meta catalog contains the still-existing Qt translations that
were included in the \c qt_ catalog in Qt 4. It was created to make porting
applications from Qt 4 to Qt 5 easier. The meta catalog depends on
translations that might be absent, because they belong to unnecessary or
deprecated modules, which might cause the loading of the translations to
fail. If you use modules that are new in Qt 5 in your application, you must
specify the names of the catalogs for those modules even if you use the
meta catalog.
The following table lists the translation catalogs available for the Qt
modules and tools in Qt.
\table
\header
\li Qt Module or Tool
\li Catalog
\row
\li \l {Qt Assistant Manual}{Qt Assistant}
\li \c assistant_
\row
\li \l [QtBluetooth]{Qt Bluetooth}
\li \c qtconnectivity_
\row
\li \l [QtConcurrent]{Qt Concurrent}
\li \c qtbase_
\row
\li \l [QtCore]{Qt Core}
\li \c qtbase_
\row
\li \l [QtDBus]{Qt D-Bus}
\li \c qtbase_
\row
\li \l {Qt Designer}
\li \c designer_
\row
\li \l [QtGui]{Qt GUI}
\li \c qtbase_
\row
\li \l {Qt Help}
\li \c qt_help_
\row
\li \l {Qt Linguist Manual}{Qt Linguist}
\li \c linguist_
\row
\li \l [QtLocation]{Qt Location}
\li \c qtlocation_
\row
\li \l [QtMultimedia]{Qt Multimedia}
\li \c qtmultimedia_
\row
\li \l [QtMultimediaWidgets]{Qt Multimedia Widgets}
\li \c qtmultimedia_
\row
\li \l[QtNfc]{Qt NFC}
\li \c qtconnectivity_
\row
\li \l[Qt Network]{Qt Network}
\li \c qtbase_
\row
\li \l [QtPositioning]{Qt Positioning}
\li \c qtlocation_
\row
\li \l [QtPrintSupport]{Qt Print Support}
\li \c qtbase_
\row
\li \l {Qt QML}
\li \c qtdeclarative_
\row
\li \l {Qt Quick}
\li \c qtdeclarative_
\row
\li \l {Qt Quick Controls}
\li \c qtquickcontrols2_
\row
\li \l {Qt Quick Widgets C++ Classes}{Qt Quick Widgets}
\li \c qtdeclarative_
\row
\li \l [QtSerialPort]{Qt Serial Port}
\li \c qtserialport_
\row
\li \l [QtSql]{Qt SQL}
\li \c qtbase_
\row
\li \l [QtWebEngine]{Qt WebEngine}
\li \c qtwebengine_
\row
\li \l [QtWebSockets]{Qt WebSockets}
\li \c qtwebsockets_
\row
\li \l [QtWidgets]{Qt Widgets}
\li \c qtbase_
\endtable
\omit
The following modules are not listed above because they are deprecated,
documented as a part of another module, QPA modules, or not translated
for some reason.
\list
\row \li QtEglFSDeviceIntegration \li \c qtbase_ \li QPA
\row \li QtMultimediaGstTools \li \c qtmultimedia_ \li Qt Multimedia
\row \li QtMultimediaQuick \li \c qtmultimedia_ \li Qt Multimedia
\row \li QtOpenGL \li \c qtbase_ \li Deprecated
\row \li QtOpenGLExtensions \li \c qtbase_ \li Deprecated
\row \li QtPacketProtocol \li \c qtdeclarative_ \li Qt Quick
\row \li QtPositioningQuick \li \c qtlocation_ \li Qt Positioning
\row \li QtQmlDebug \li \c qtdeclarative_ \li Qt Quick
\row \li QtQmlModels \li \c qtdeclarative_ \li Qt Quick
\row \li QtQmlWorkerScript \li \c qtdeclarative_ \li Qt Quick
\row \li QtQuickParticles \li \c qtdeclarative_ \li Qt Quick
\row \li QtQuickShapes \li \c qtdeclarative_ \li Qt Quick
\row \li QtQuickTemplates2 \li \c qtquickcontrols2_ \li Qt Quick Controls 2
\row \li QtQuickTest \li \c qtdeclarative_ \li Not translated
\row \li QtQuickWidgets \li \c qtdeclarative_ \li Qt Quick
\row \li QtScript \li \c qtscript_ \li Deprecated
\row \li QtScriptTools \li \c qtscript_ \li Deprecated
\row \li QtTest \li \c qtbase_ \li Not translated
\row \li QtWebEngineCore \li \c qtwebengine_ \li Qt WebEngine
\row \li QtWebEngineWidgets \li \c qtwebengine_ \li Qt WebEngine
\row \li QtXml \li \c qtbase_ \li Deprecated
\row \li QtXmlPatterns \li \c qtxmlpatterns_ \li Deprecated
\endlist
\endomit
\section2 Example: Basic Qt Modules
For example, to locate translations for basic Qt modules, such as Qt Core,
Qt GUI, Qt Network, and Qt Widgets, add the following code to the \c main()
function:
\snippet snippets/code/doc_src_i18n.cpp 14
\section1 Support for Encodings
The QTextCodec class and the facilities in QTextStream make it easy to
support many legacy 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 external 8-bit data. QTextCodec::codecForLocale()
returns a codec that can be used to convert between this locale encoding
and Unicode.
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 snippets/code/doc_src_i18n.cpp 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 \l{http://www.ietf.org/rfc/rfc2279.txt}{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 snippets/code/doc_src_i18n.cpp 10
Unicode I/O should be used as this maximizes the portability
of documents between users around the world. In many cases it is
however still necessary to support other encodings as your users will
need to process existing documents. The most important additional
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
\section1 Localizing Numbers, Dates, Times and Currency
Localization is the process of adapting to local conventions, for
example presenting dates and times using the locally preferred
formats. For localized numbers, dates, times and currency strings, 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 QTranslator objects, 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 snippets/code/doc_src_i18n.cpp 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.
\l{QEvent::LanguageChange}{LanguageChange} events are posted when a new
translation is installed using the QCoreApplication::installTranslator()
function. Additionally, other application components can also force
widgets to update themselves by posting LanguageChange events to them.
\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
\li Locale-oriented fonts and input methods. Qt hides these and
provides Unicode input and output.
\li Filesystem conventions such as UTF-8
are today used by default in most 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).
\li File I/O defaults to the local 8-bit encoding,
with Unicode options in QTextStream.
\li Some older 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 to have Japanese fonts installed, 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 Linux
\list
\li Qt provides full Unicode support, including input methods, fonts,
clipboard, drag-and-drop.
\li The file system is usually encoded in UTF-8 on all modern Linux
distributions and should not pose a problem. File I/O defaults to UTF-8.
\endlist
\section2 Windows
\list
\li Qt provides full Unicode support, including input methods, fonts,
clipboard, drag-and-drop and file names.
\li 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.
\endlist
\section2 \macos
For details on \macos-specific translation, refer to the Qt for macOS issues
document \l{Qt for macOS - Specific Issues#Translating the Application Menu and Native Dialogs}{here}.
\section1 Related Pages
*/
/*!
\page i18n-source-translation.html
\title Writing Source Code for Translation
\ingroup internationalization
\previouspage Internationalization with Qt
\nextpage Translation Rules for Plurals
\brief How to write source code in a way that makes it possible for user-visible text to be translated.
\tableofcontents
Writing cross-platform international software with Qt is a gentle,
incremental process. Your software can become internationalized in
the stages described in the following sections.
For more information about internalizing Qt Quick application, see
\l{Internationalization and Localization with Qt Quick}.
\section1 Using 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 \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 easier versions of the crude
\c{const char *} and \c char from traditional C.
\c{char *} strings in source code are assumed to be
\l{http://www.ietf.org/rfc/rfc2279.txt}{UTF-8} encoded when being
implicitly converted to a QString. If your C string literal
uses a different encoding, use QString::fromLatin1() or QTextCodec
to convert the literal to a Unicode encoded QString.
\section1 Using tr() for All Literal Text
Wherever your program uses a string literal (quoted 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 the \l{QObject::}{tr()} function to obtain
translated text for your classes, typically for display purposes. This
function is also used to indicate which text strings in an application are
translatable.
For example, assuming the \c LoginWidget is a subclass of QWidget:
\snippet snippets/code/doc_src_i18n.cpp 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 snippets/code/doc_src_i18n.cpp 1
Qt indexes each translatable string by the \e{translation context} it is
associated with; this is generally the name of the QObject subclass it is
used in.
Translation contexts are defined for new QObject-based classes by the use
of the Q_OBJECT macro in each new class definition.
When tr() is called, it looks up the translatable string using a QTranslator
object. For translation to work, one or more of these must have been
installed on the application object in the way described in
\l{Enabling Translation}.
Translating strings in QML works exactly the same way as in C++, with the only
difference being that you need to call qsTr() instead of \l{QObject::}{tr()}. See also
the page on \l{Internationalization and Localization with Qt Quick}.
\section1 Defining a Translation Context
The translation context for QObject and each QObject subclass is the
class name itself. Developers subclassing QObject must use the
Q_OBJECT macro in their class definition to override the translation
context. This macro sets the context to the name of the subclass.
For example, the following class definition includes the Q_OBJECT macro,
implementing a new tr() that uses the \c MainWindow context:
\code
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow();
\endcode
\dots
If Q_OBJECT is not used in a class definition, the context will be
inherited from the base class. For example, since all QObject-based
classes in Qt provide a context, a new QWidget subclass defined without
a Q_OBJECT macro will use the \c QWidget context if its tr() function
is invoked.
\section1 Using tr() to Obtain a Translation
The following example shows how a translation is obtained for the
class shown in the previous section:
\code
void MainWindow::createMenus()
{
fileMenu = menuBar()->addMenu(tr("&File"));
\endcode
\dots
Here, the translation context is \c MainWindow because it is the
\c MainWindow::tr() function that is invoked. The text returned
by the tr() function is a translation of "&File" obtained from
the \c MainWindow context.
When Qt's translation tool, \l{Using lupdate}{lupdate}, is used to process
a set of source
files, the text wrapped in tr() calls is stored in a section of the translation
file that corresponds to its translation context.
In some situations, it is useful to give a translation context explicitly
by fully qualifying the call to tr(); for example:
\snippet snippets/code/src_corelib_kernel_qobject.cpp explicit tr context
This call obtains the translated text for "Page up" from the \c QScrollBar
context. Developers can also use the QCoreApplication::translate() function
to obtain a translation for a particular translation context.
\section1 Using tr() to Localize Numbers
You can localize numbers by using appropriate tr() strings:
\snippet snippets/code/doc_src_i18n.cpp 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 to make
the code use the 24-hour clock branch.
\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 snippets/i18n-non-qt-class/myclass.h 0
\dots
\snippet 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 Translator Comments
Developers can include information about each translatable string to
help translators with the translation process. These are extracted
when \c lupdate is used to process the source files. The recommended
way to add comments is to annotate the tr() calls in your code with
comments of the form:
\tt{//: ...}
or
\tt{\begincomment: ... \endcomment}
Examples:
\snippet snippets/code/src_corelib_kernel_qobject.cpp 40
In these examples, the comments will be associated with the strings
passed to tr() in the context of each call.
\section1 Adding Meta-Data to Strings
Additional data can be attached to each translatable message. These are
extracted when \c lupdate is used to process the source files. The
recommended way to add meta-data is to annotate the tr() calls in your code
with comments of the form:
\tt{//= <id>}
This can be used to give the message a unique identifier to support tools
which need it.
An alternative way to attach meta-data is to use the following syntax:
\tt{//~ <field name> <field contents>}
This can be used to attach meta-data to the message. The field name should
consist of a domain prefix (possibly the conventional file extension of the
file format the field is inspired by), a hyphen and the actual field name
in underscore-delimited notation. For storage in TS files, the field name
together with the prefix "extra-" will form an XML element name. The field
contents will be XML-escaped, but otherwise appear verbatim as the
element's contents. Any number of unique fields can be added to each
message.
Example:
\snippet snippets/code/src_corelib_kernel_qobject.cpp meta data
You can use the keyword \e TRANSLATOR for translator comments.
Meta-data appearing right in front of the TRANSLATOR keyword applies to
the whole TS file.
\section1 Disambiguation
If the same translatable string is used in different roles within the same
translation context, an additional identifying string may be passed in
the call to \l{QObject::}{tr()}. This optional disambiguation argument
is used to distinguish between otherwise identical strings.
Example:
\snippet snippets/code/src_corelib_kernel_qobject.cpp 17
\dots
In Qt 4.4 and earlier, this disambiguation parameter was the preferred
way to specify comments to translators.
\section1 Handling Plurals
Some translatable strings contain placeholders for integer values and need
to be translated differently depending on the values in use.
To help with this problem, developers pass an additional integer argument
to the \l{QObject::}{tr()} function, and typically use a special notation
for plurals in each translatable string.
If this argument is equal or greater than zero, all occurrences of
\c %n in the resulting string are replaced with a decimal representation
of the value supplied. In addition, the translation used will adapt to the
value according to the rules for each language.
Example:
\snippet snippets/code/src_corelib_kernel_qobject.cpp 18
The table below shows what string is returned depending on the
active translation:
\table
\header \li \li{3,1} Active Translation
\header \li \a n \li No Translation \li French \li English
\row \li 0 \li "0 message(s) saved" \li "0 message sauvegard\unicode{0xE9}" \li "0 message\b{s} saved"
\row \li 1 \li "1 message(s) saved" \li "1 message sauvegard\unicode{0xE9}" \li "1 message saved"
\row \li 2 \li "2 message(s) saved" \li "2 message\b{s} sauvegard\unicode{0xE9}\b{s}" \li "2 message\b{s} saved"
\row \li 37 \li "37 message(s) saved" \li "37 message\b{s} sauvegard\unicode{0xE9}\b{s}" \li "37 message\b{s} saved"
\endtable
This idiom is more flexible than the traditional approach; e.g.,
\snippet snippets/code/src_corelib_kernel_qobject.cpp 19
because it also works with target languages that have several
plural forms (e.g., Irish has a special "dual" form that should
be used when \c n is 2), and it handles the \e n == 0 case
correctly for languages such as French that require the singular.
To handle plural forms in the native language, you need to load a
translation file for this language, too. The lupdate tool has the
\c -pluralonly command line option, which allows the creation of
TS files containing only entries with plural forms.
See the \l{Qt Quarterly} Article
\l{http://doc.qt.io/archives/qq/qq19-plurals.html}
{Plural Forms in Translations} for further details on this issue.
Instead of \c %n, you can use \c %Ln to produce a localized
representation of \a n. The conversion uses the default locale,
set using QLocale::setDefault(). (If no default locale was
specified, the system wide locale is used.)
A summary of the rules used to translate strings containing plurals can be
found in the \l{Translation Rules for Plurals} document.
\section1 Translating Text That is Outside of a QObject Subclass
\section2 Using QCoreApplication::translate()
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 snippets/code/doc_src_i18n.cpp 13
\section2 Using QT_TR_NOOP() and QT_TRANSLATE_NOOP() in C++
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 tool. The macros expand to
just the text (without the context).
Example of QT_TR_NOOP():
\snippet snippets/code/doc_src_i18n.cpp 2
Example of QT_TRANSLATE_NOOP():
\snippet snippets/code/doc_src_i18n.cpp 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::fromUtf8() and QString::fromLatin1()
for more information.
\section1 Using QKeySequence() for Accelerator Values
Accelerator values such as Ctrl+Q or Alt+F need to be translated
too. If you hardcode \c{Qt::CTRL + Qt::Key_Q} for "quit" in your
application, translators won't be able to override it. The
correct idiom is:
\code
exitAct = new QAction(tr("E&xit"), this);
exitAct->setShortcuts(QKeySequence::Quit);
\endcode
\section1 Using Numbered Arguments
The QString::arg() functions offer a simple means for substituting
arguments:
\snippet snippets/code/doc_src_i18n.cpp 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 snippets/code/doc_src_i18n.cpp 5
produces the correct output in English and Norwegian:
\snippet snippets/code/doc_src_i18n.qdoc 6
\section1 Further Reading
\l{Qt Linguist Manual}, \l{Hello tr() Example}, \l{Translation Rules for Plurals}
*/
/*!
\page i18n-plural-rules.html
\title Translation Rules for Plurals
\ingroup internationalization
\previouspage Writing Source Code for Translation
\brief A summary of the translation rules for plurals produced by Qt's i18n tools.
The table below shows the specific rules that are produced by Qt Linguist
and \c lrelease for a selection of languages. Cells marked \e otherwise
indicate the form used when none of the other rules are appropriate for a
specific language.
\table 80%
\header \li Language \li Rule 1 \li Rule 2 \li Rule 3
\row \li English \li \c{n == 1}
\li \e{otherwise} \li N/A
\row \li French \li \c{n < 2}
\li \e{otherwise} \li N/A
\row \li Czech \li \c{n % 100 == 1}
\li \c{n % 100 >= 2 && n % 100 <= 4}
\li \e{otherwise}
\row \li Irish \li \c{n == 1}
\li \c{n == 2} \li \e{otherwise}
\row \li Latvian \li \c{n % 10 == 1&& n % 100 != 11}
\li \c{n != 0} \li \e{otherwise}
\row \li Lithuanian \li \c{n % 10 == 1&& n % 100 != 11}
\li \c{n % 100 != 12 && n % 10 == 2}
\li \e{otherwise}
\row \li Macedonian \li \c{n % 10 == 1}
\li \c{n % 10 == 2} \li \e{otherwise}
\row \li Polish \li \c{n == 1}
\li \c{n % 10 >= 2 && n % 10 <= 4
&& (n % 100 < 10 || n % 100 > 20)}
\li \e{otherwise}
\row \li Romanian \li \c{n == 1}
\li \c{n == 0|| (n % 100 >= 1 && n % 100 <= 20)}
\li \e{otherwise}
\row \li Russian \li \c{n % 10 == 1&& n % 100 != 11}
\li \c{n % 10 >= 2 && n % 10 <= 4
&& (n % 100 < 10 || n % 100 > 20)}
\li \e{otherwise}
\row \li Slovak \li \c{n == 1} \li \c{n >= 2 && n <= 4}
\li \e{otherwise}
\row \li Japanese \li \e{otherwise} \li N/A \li N/A
\endtable
The rules themselves are not documented and are internal to Qt Linguist and \c lrelease.
*/