Internationalization and Localization with Qt Quick Ultralite

Based on Qt

The functionality in Qt Quick Ultralite is based on Internationalization and Localization in Qt and Qt Linguist. This document describes the differences, enhancements, and limitations compared to Qt.


Use either the qsTr() or qsTrId() function in QML files to mark string literals for translation. All such marked string literals are found by the Qt Linguist tool, which generates the translation source file (.ts) containing those strings.

Important: Use one of these two alternatives in an application. Using both of them in an application may lead to unexpected behavior.

Once translations are made, there will a .ts file for each language. These files are compiled to translation release files (.qm) and passed to the QML compiler, which replaces the qsTr() or qsTrId() calls with a lookup of the correct string based on the Qt.uiLanguage property.

The Qt.uiLanguage property can also be used in other bindings to make decisions based on the active language.

The translation example shows how to use qsTr() and the Qt.uiLanguage property.

Building with CMake

Listing the translation source files for the target languages in the TranslationFiles.files QmlProject property and using the containing QmlProject file in qul_add_target with QML_PROJECT specified will have two effects:

  • It creates a update_translations CMake target which is not included in the default build. Trigger a build of this target to create or update the .ts files with new and changed translatable strings from the source code.
  • It sets up the build system to embed the translations from the .ts files in the program binary.

Each .ts file introduces a translated language that can be switched to at runtime by setting the Qt.uiLanguage property. The name of the language is derived from the name of the .ts file. For example, the "app_nb_NO.ts" file defines the translations for nb_NO, which is the ISO language code for Norwegian Bokmål.

When the Qt.uiLanguage is empty, no translation is applied and the strings used in the source code are shown.

If an application does not support multiple languages, set the TranslationFiles.MCU.omitSourceLanguage to false.

Standalone qmlprojectexporter

When developing using a build system other than CMake, qmlprojectexporter can be run solely to update the translations, refer to qmlprojectexporter's update translation argument for more details.

Text ID based translations

The text ID translation mechanism is an industrial strength system for internationalization and localization. Each text in the application has a unique identifier (text ID) that you use in the source code instead of text. This makes it much easier to manage large numbers of translated texts.

If you set the idBasedTranslations to true in the .qmlproject file, it will enable text ID based translations for your project. Use the qsTrId() function instead of qsTr() in QML files to mark strings for text ID based translations.

Note: You must use only plain text based or only text ID based functions in one application. If you mix them, you will end up with an incomplete set of texts to be translated. If QML modules in your application have QML files to be translated, the QML modules should follow the same translation mechanism as the main project.

Memory optimization

When using ID-based translations, the application is not expected to display the source strings. It is highly recommended to set the TranslationFiles.MCU.omitSourceLanguage flag to true to reduce ROM footprints when idBasedTranslations is enabled.

Qt Design Studio translations

Qt Design Studio can create and maintain translations using the Translations view. When using this feature, Qt Design Studio will automatically update the .qmlproject file to include the translations in the application.

Note: Make sure to generate translation files from Qt Design Studio before running qmlprojectexporter.


The following functionality is not currently supported:

  • Translation of strings in C++ files
  • Text ID based translations with CMake
  • Translation functions other than qsTr() or qsTrId(), such as qsTranslate(), QT_TR_NOOP(), QT_TRANSLATE_NOOP() and QT_TRID_NOOP()
  • The plural disambiguation argument in qsTr() or qsTrId()

Available under certain Qt licenses.
Find out more.