CMake: Add I18N_LANGUAGES keyword to qt_standard_project_setup

[ChangeLog][CMake] Added variable QT_I18N_LANGUAGES to specify the
languages that are used for i18n in the project.

[ChangeLog][CMake] Added keyword I18N_LANGUAGES to
qt_standard_project_setup to conveniently set QT_I18N_LANGUAGES.

The call
  qt_standard_project_setup(I18N_LANGUAGES hi ho)
sets the variable QT_I18N_LANGUAGES.

The target finalizers use this variable to set up CFBundleLocalizations
on Apple platforms.

qt_add_translations will be extended to read QT_I18N_LANGUAGES as well
to determine the names of .ts files if TS_FILES is not given.

Fixes: QTBUG-116716
Change-Id: I76f0753d10efb9c32947d9239e43382c9d85eb51
Reviewed-by: Amir Masoud Abdol <amir.abdol@qt.io>

cmake/QtPublicAppleHelpers.cmake

@@ -618,9 +618,12 @@ function(_qt_internal_set_apple_localizations target)
         return()
     endif()
 
-    get_target_property(supported_languages "${target}" _qt_apple_supported_languages)
-    if("${supported_languages}" STREQUAL "supported_languages-NOTFOUND")
-        return()
+    set(supported_languages "${QT_I18N_LANGUAGES}")
+    if("${QT_I18N_LANGUAGES}" STREQUAL "")
+        get_target_property(supported_languages "${target}" _qt_apple_supported_languages)
+        if("${supported_languages}" STREQUAL "supported_languages-NOTFOUND")
+            return()
+        endif()
     endif()
     get_target_property(plist_file "${target}" MACOSX_BUNDLE_INFO_PLIST)
     if (NOT plist_file)

src/corelib/Qt6CoreMacros.cmake

@@ -2969,7 +2969,9 @@ macro(qt6_standard_project_setup)
             REQUIRES
             SUPPORTS_UP_TO
         )
-        set(__qt_sps_args_multi)
+        set(__qt_sps_args_multi
+            I18N_LANGUAGES
+        )
         cmake_parse_arguments(__qt_sps_arg
             "${__qt_sps_args_option}"
             "${__qt_sps_args_single}"
@@ -3068,6 +3070,11 @@ macro(qt6_standard_project_setup)
                 set_property(GLOBAL PROPERTY AUTOGEN_TARGETS_FOLDER ${__qt_qt_targets_folder})
             endif()
         endif()
+
+        # I18N support.
+        if(DEFINED __qt_sps_arg_I18N_LANGUAGES AND NOT DEFINED QT_I18N_LANGUAGES)
+            set(QT_I18N_LANGUAGES ${__qt_sps_arg_I18N_LANGUAGES})
+        endif()
     endif()
 endmacro()
 

src/corelib/doc/src/cmake/cmake-configure-variables.qdoc

@@ -477,6 +477,35 @@ methods provided by CMake.
 \sa {qt6_standard_project_setup}{qt_standard_project_setup()}
 */
 
+/*!
+\page cmake-variable-qt-i18n-languages.html
+\ingroup cmake-variables-qtcore
+
+\title QT_I18N_LANGUAGES
+\target cmake-variable-QT_I18N_LANGUAGES
+
+\summary {List of languages to be used for project internationalization}
+
+\cmakevariablesince 6.7
+
+This variable specifies a list of languages that are used for project
+internationalization. The single languages must be compatible with the
+string-based \l QLocale constructor.
+
+The languages in \c QT_I18N_LANGUAGES are used to
+\list
+    \li Set up executable targets for consuming \c{.qm} files.
+    \li Automatically construct \c{.ts} file names in
+        \l{qt6_add_translations}{qt_add_translations()}.
+\endlist
+
+This variable can be conveniently set with the
+{qt6_standard_project_setup}{qt_standard_project_setup()} command.
+
+\sa {qt6_standard_project_setup}{qt_standard_project_setup()}
+\sa {qt6_add_translations}{qt_add_translations()}
+*/
+
 /*!
 \page cmake-variable-qt-ios-launch-screen.html
 \ingroup cmake-variables-qtcore

src/corelib/doc/src/cmake/qt_standard_project_setup.qdoc

@@ -20,6 +20,7 @@
 qt_standard_project_setup(
     [REQUIRES <version>]
     [SUPPORTS_UP_TO <version>]
+    [I18N_LANGUAGES <language...>]
 )
 \endcode
 
@@ -81,6 +82,12 @@ setting the \l{QT_NO_STANDARD_PROJECT_SETUP} variable to true.
 \sa {qt6_generate_deploy_app_script}{qt_generate_deploy_app_script()}
 \sa qt_policy
 
+\section1 Internationalization
+
+Since Qt 6.7, it is possible to specify the languages that are used for project
+internationalization with the \c I18N_LANGUAGES argument. See \l
+QT_I18N_LANGUAGES for details.
+
 \section1 Example
 
 \include cmake-generate-deploy-app-script.qdocinc