[PyQt] How To Internationalization (i18n)?

Step by step, it’s time to skip a lot of boring explainations and just start with examples quickly:

self.tr()

Use self.tr() to surround all strings needed to be translated in Python code. (Must be in a QWidget class). For example:

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from PyQt4 import QtCore, QtGui
class MainWindow(QtGui.QMainWindow):
    def __init__(self, parent=None):
        super().__init__()
        label = QtGui.QLabel(self.tr("Apple"))
        self.setCentralWidget(label)

if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)

    main_window  = MainWindow(app)
    main_window.show()

    app.exec_()

QTranslator()

Take zh_TW for example, install QTranslator() in QApplication(). Use QTranslator().load() to load translate file.

bool QTranslator.load (self, QString fileName, QString directory = QString(), QString searchDelimiters = QString(), QString suffix = QString())
bool QTranslator.load (self, QLocale locale, QString fileName, QString prefix = QString(), QString directory = QString(), QString suffix = QString())

Notice: the file QTranslator loads is a .qm file (a binary file generate from .ts), instead of a .ts.

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translator = QtCore.QTranslator()
translator.load("translate/zh_TW.qm")
app.installTranslator(translator)

Get System Locale Information

- QTranslator Class Reference
- QLocale Class Reference

Beside to os.getenv(), you can also get current system’s locale name with QtCore.QLocale.system().name(), its return value is a string like ja_JP. So you can load translation file by system’s locale:

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print('Localization loaded: '
      ,translator.load(QtCore.QLocale.system().name() + '.qm', 'translate')) # name, dir

pylupdate To Create .ts File

Now create a directory translate/, then use pylupdate to generate an empty .ts file in it for your PyQt file:

$ pylupdate4 main.py -ts translate/zh_TW.ts

Time To Translate!

Open translate/zh_TW.ts with Qt Linguist and begin to translate.

you can also use your prefered text editor to edit the file directly, because it’s just a XML file.

lrelease To Convert .ts into .qm

After finishing the translating, use lrelease to generate .qm binary file from .ts.

$ lrelease translate/zh_TW.ts
Updating 'translate/zh_TW.qm'...
Generated 55 translation(s) (55 finished and 0 unfinished)

But, How To Update Translation File?

After modifying strings in PyQt file, updating the translation file is necessary.

First, use pylupdate to update .ts file:

$ pylupdate4 main.py -ts translate/zh_TW.ts

Now you can open the .ts file with Qt Linguist to update old translations. After that, use lrelease again to generate .qm.

$ lrelease translate/zh_TW.ts
Updating 'translate/zh_TW.qm'...
Generated 56 translation(s) (56 finished and 0 unfinished)

At last, maybe you want to totally remove the unused/obsoleted translation items in .ts file, use -noobsolete option to do this:

$ pylupdate4 main.py -ts -noobsolete translate/zh_TW.ts

[2014-09-03 水 17:24] Start
[2014-09-03 水 18:00] Dinner time.
[2014-09-03 水 19:14] Done.
[2014-09-03 水 21:07] Add system locale.
[2014-09-04 木 08:28] Typo