diff --git a/src/corelib/Qt6CoreMacros.cmake b/src/corelib/Qt6CoreMacros.cmake
index ed3b4534999..8a0d07feac7 100644
--- a/src/corelib/Qt6CoreMacros.cmake
+++ b/src/corelib/Qt6CoreMacros.cmake
@@ -3264,7 +3264,10 @@ macro(qt6_standard_project_setup)
                 AND NOT DEFINED QT_I18N_TRANSLATED_LANGUAGES)
             set(QT_I18N_TRANSLATED_LANGUAGES ${__qt_sps_arg_I18N_TRANSLATED_LANGUAGES})
         endif()
-        if(DEFINED __qt_sps_arg_I18N_SOURCE_LANGUAGE AND NOT DEFINED QT_I18N_SOURCE_LANGUAGE)
+        if(NOT DEFINED __qt_sps_arg_I18N_SOURCE_LANGUAGE)
+            set(__qt_sps_arg_I18N_SOURCE_LANGUAGE en)
+        endif()
+        if(NOT DEFINED QT_I18N_SOURCE_LANGUAGE)
             set(QT_I18N_SOURCE_LANGUAGE ${__qt_sps_arg_I18N_SOURCE_LANGUAGE})
         endif()
     endif()
diff --git a/src/corelib/doc/src/cmake/cmake-configure-variables.qdoc b/src/corelib/doc/src/cmake/cmake-configure-variables.qdoc
index d171cc8509e..5773650163d 100644
--- a/src/corelib/doc/src/cmake/cmake-configure-variables.qdoc
+++ b/src/corelib/doc/src/cmake/cmake-configure-variables.qdoc
@@ -516,6 +516,8 @@ The languages in \c QT_I18N_TRANSLATED_LANGUAGES are used to:
 This variable can be conveniently set with the
 \l {qt6_standard_project_setup}{qt_standard_project_setup()} command.
 
+By default, translatable strings are considered to be written in \c{en}.
+
 \sa {qt6_standard_project_setup}{qt_standard_project_setup()}
 \sa {qt6_add_translations}{qt_add_translations()}
 */
diff --git a/src/corelib/doc/src/cmake/qt_standard_project_setup.qdoc b/src/corelib/doc/src/cmake/qt_standard_project_setup.qdoc
index 867fb00ca0b..59b33f599cc 100644
--- a/src/corelib/doc/src/cmake/qt_standard_project_setup.qdoc
+++ b/src/corelib/doc/src/cmake/qt_standard_project_setup.qdoc
@@ -90,7 +90,8 @@ internationalization with the \c I18N_TRANSLATED_LANGUAGES argument. See \l
 QT_I18N_TRANSLATED_LANGUAGES for details.
 
 Use I18N_SOURCE_LANGUAGE to specify the language that translatable strings are
-written in. See \l QT_I18N_SOURCE_LANGUAGE for details.
+written in. By default, \c en is used. See \l QT_I18N_SOURCE_LANGUAGE for
+details.
 
 \section1 Example