Writing Source Code for Translation

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 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 %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:

 int n = messages.count();
 showMessage(tr("%n message(s) saved", "", n));

The table below shows what string is returned depending on the active translation:

This idiom is more flexible than the traditional approach; e.g.,

 n == 1 ? tr("%n message saved") : tr("%n messages saved")

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 n is 2), and it handles the n == 0 case correctly for languages such as French that require the singular. See the Qt Linguist Manual for details.

Instead of %n, you can use %Ln to produce a localized representation of n. The conversion uses the default locale, set using QLocale::setDefault(). (If no default locale was specified, the "C" locale is used.)

A summary of the rules used to translate strings containing plurals can be found in the Translation Rules for Plurals document.

 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);

     QTranslator qtTranslator;
     qtTranslator.load("qt_" + QLocale::system().name(),
             QLibraryInfo::location(QLibraryInfo::TranslationsPath));
     app.installTranslator(&qtTranslator);

     QTranslator myappTranslator;
     myappTranslator.load("myapp_" + QLocale::system().name());
     app.installTranslator(&myappTranslator);

     ...
     return app.exec();
 }