Qt Linguist Manual: Release Manager

Translation files consist of all the user-visible text and Ctrl key accelerators in an application and translations of that text.

To create translation files:

1. Run lupdate to generate the first set of translation source (TS) files with all the user-visible text but no translations.

2. Give the TS files to the translator who adds translations using Qt Linguist. Qt Linguist takes care of any changed or deleted source text.

3. Run lupdate to incorporate any new text added to the application. lupdate synchronizes the user-visible text from the application with the translations. It does not destroy any data.

4. To release the application, run lrelease to read the TS files and produce the QM files used by the application at runtime.

For lupdate to work successfully, it must know which translation files to produce. The files are listed in the application's .pro Qt project file.

Usage: lupdate myproject.pro

The lupdate command line tool finds the translatable strings in the specified source, header and Qt Designer interface files, and produces or updates .ts translation files. The files to process and the files to update can be set at the command line, or provided in a .pro file specified as a command line argument. The developer creates the .pro file, as described in Qt Linguist Manual: Developers.

You can generate the translation file for a single QML file in the following way:

lupdate main.qml -ts main_en.ts

To make a translation file for another language, for example French, you copy main_en.ts to main_fr.ts, and translate the strings in the French TS file.

lupdate processes QML files that are listed in the .qrc file:

RESOURCES += qml.qrc

To have all QML files processed by lupdate:

lupdate application.qrc -ts myapp_en.ts

You can also process all QML files without using a .qrc file:

lupdate -extensions qml -ts myapp_en.ts

If you are mostly processing QML files, but also have C++ code that contains strings to be translated, you can add it in the same command:

lupdate qml.qrc filevalidator.cpp -ts myapp_en.ts

The translation files can be mentioned in the .pro file, but it is also possible to do without it, and just specify the translation file on the command line.

For example, to generate .ts files that will be used for English and French:

lupdate qml.qrc filevalidator.cpp -ts myapp_en.ts myapp_fr.ts

The produced translation files are given to the translator who uses Qt Linguist to read the files and insert the translations.

Companies that have their own translators in-house may find it useful to run lupdate regularly, perhaps monthly, as the application develops. This will lead to a fairly low volume of translation work spread evenly over the life of the project and will allow the translators to support a number of projects simultaneously.

Companies that hire in translators as required may prefer to run lupdate only a few times during the application life cycle. The first time might be just before the first test phase. This will provide the translator with a substantial single block of work and any bugs that the translator detects may easily be included with those found during the initial test phase. The second and any subsequent lupdate runs would probably take place during the final beta phase.

The TS file format is a simple human-readable XML format that can be used with version control systems if required. lupdate can also process Localization Interchange File Format (XLIFF) format files; files in this format typically have file names that end with the .xlf suffix.

Pass the -help option to lupdate to view supported options.

Qt Linguist is also able to import and export XLIFF files. See the Translators section for more information.

Usage: lrelease myproject.pro

The lrelease command line tool produces QM files out of TS files. The QM file format is a compact binary format that is used by the localized application. It provides extremely fast lookups for translations. The TS files lrelease processes can be specified at the command line, or given indirectly by a Qt .pro project file.

This tool is run whenever a release of the application is to be made, from initial test version through to final release version. If the QM files are not created, for example because an alpha release is required before any translation has been undertaken, the application will run perfectly well using the text the developers placed in the source files. Once the QM files are available the application will detect them and use them automatically.

lrelease can be also be run without specifying a .pro file:

lrelease.exe main_en.ts languages\main_fr.ts

Pass the -help option to lrelease to view supported options.

Both lupdate and lrelease may be used with TS translation source files which are incomplete. Missing translations will be replaced with the native language phrases at runtime.