{"id":11337,"date":"2024-10-01T10:43:01","date_gmt":"2024-10-01T08:43:01","guid":{"rendered":"https:\/\/www.basyskom.de\/?p=11337"},"modified":"2024-10-01T10:47:34","modified_gmt":"2024-10-01T08:47:34","slug":"translating-qt-applications","status":"publish","type":"post","link":"https:\/\/www.basyskom.de\/en\/translating-qt-applications\/","title":{"rendered":"Translating Qt Applications"},"content":{"rendered":"
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Translating Qt Applications<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Translating a Qt application, executing the right tool at the right time, can be a daunting task. This blog post gives an overview of the differences between what it was like during the Qt 5 times, how Qt 6 improved upon it and what new functionality Qt 6.7 brings.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Generally, there\u2019s two tools involved: lupdate<\/strong> and lrelease<\/strong>.<\/p>

  • lupdate<\/strong>, extracts translatable strings from your source code by scanning it for the relevant keywords (qsTr, tr, QT_TR_NOOP<\/strong> and others) and places them in a `.ts` file, either creating a new one or updating an existing one. Those `.ts` files are XML files that can be edited in Qt Linguist or sent to a translation service company.<\/li>
  • lrelease<\/strong> converts them into binary `.qm` files that get bundled with and loaded by the application.<\/li><\/ul>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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    The Qt 5.15 way <\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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    Qt has always provided CMake API for dealing with `lupdate<\/strong>` and `lrelease<\/strong>` in the `LinguistTools<\/strong>` package. In Qt 5 days you typically found yourself using:<\/p>

    • `qt_create_translation<\/strong>` runs `lupdate` and creates or updates the `.ts` files<\/li>
    • `qt_add_translation<\/strong>` runs `lrelease` and converts the `.ts` files to `.qm` files for consumption by the application<\/li><\/ul>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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      However, it was your responsibility to run the right commands at the proper time. You probably don\u2019t want to update translations during every build to avoid cluttering the translation files with temporary changes. Therefore, you either had to add a custom build target or add a CMake option and build with something custom like `-UPDATE_TS_FILES=ON<\/strong>`. As was custom at the time, both CMake commands return the list of `.qm` files in a variable that you then have to add to your project sources and\/or application resources. Additionally, you had to manually take care of the list of languages you wanted to support.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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      The Qt 6 way <\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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      Enter Qt 6: CMake has become the default<\/em> and recommended build system generator for Qt projects and building Qt itself. Therefore, Qt has a vested interest in providing good CMake API for all its features and `LinguistTools<\/strong>` is no exception.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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      Note<\/strong>: There are changes on how translations are added to cmake within the Qt6 Series. We will discuss those changes down below. For a start we will describe on how it is done using Qt6.7+<\/strong>.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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      Qt 6.2<\/strong><\/span> added a new `qt_add_translations<\/span><\/em><\/strong>` command. Note the plural _s_. Keep this in mind, since the old Qt5 command is still available.
      The new qt_add_translations<\/strong> combines the previous `create` and `add` commands and adds build targets for both `lupdate` and `lrelease`.<\/p>

      A `<target>_lupdate` naturally runs `lupdate` while `<target>_lrelease` runs `release`.<\/p>

      The latter is actually built by default with your project. Additionally, a global `update_translations` and `release_translations` target is created for all translations within the project. Their names can be adjusted using the `QT_GLOBAL_LUPDATE_TARGET<\/strong>` and `QT_GLOBAL_LRELEASE_TARGET<\/strong>` variables.<\/p>

      In order to specify which languages your application supports, either set the `QT_I18N_TRANSLATED_LANGUAGES<\/strong>` variable, or use `I18N_TRANSLATED_LANGUAGES<\/strong>` argument of `qt_standard_project_setup<\/strong>`. The source language defaults to \u201cen\u201d but can be configured using `(QT_)I18N_SOURCE_LANGUAGE`.<\/p>

      Even if you merely migrate an application to the new way and have existing `.ts` files already, you want to set this variable since some platforms and distribution methods require the application to report its supported language in its metadata.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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      \nset(QT_I18N_TRANSLATED_LANGUAGES de fr)\nadd_executable(qstrtest main.cpp)\nqt_add_translation(qstrtest) <\/code><\/pre>