[FEATURE] new global expression variable $qgis_locale

Returns current locale used by QGIS. By default this is current
system locale. If user enabled locale override in QGIS settings
overriden locale will be returned.

Author: alexbruy

src/core/qgsapplication.cpp

@@ -48,6 +48,7 @@
 #include <QIcon>
 #include <QPixmap>
 #include <QThreadPool>
+#include <QLocale>
 
 #ifndef Q_OS_WIN
 #include <netinet/in.h>
@@ -902,6 +903,20 @@ QString QgsApplication::platform()
   return sPlatformName;
 }
 
+QString QgsApplication::locale()
+{
+  QSettings settings;
+  bool overrideLocale = settings.value( QStringLiteral( "locale/overrideFlag" ), false ).toBool();
+  if ( overrideLocale )
+  {
+    return settings.value( QStringLiteral( "locale/userLocale" ), QString() ).toString();
+  }
+  else
+  {
+    return QLocale::system().name().left( 2 );
+  }
+}
+
 QString QgsApplication::userThemesFolder()
 {
   return qgisSettingsDirPath() + QStringLiteral( "/themes" );

src/core/qgsapplication.h

@@ -241,6 +241,11 @@ class CORE_EXPORT QgsApplication : public QApplication
      */
     static QString platform();
 
+    /** Returns the QGIS locale.
+     * @note added in QGIS 3.0
+     */
+    static QString locale();
+
     //! Returns the path to user's themes folder
     static QString userThemesFolder();
 

src/core/qgsexpressioncontext.cpp

@@ -524,6 +524,7 @@ QgsExpressionContextScope* QgsExpressionContextUtils::globalScope()
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "qgis_release_name" ), Qgis::QGIS_RELEASE_NAME, true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "qgis_platform" ), QgsApplication::platform(), true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "qgis_os_name" ), QgsApplication::osName(), true ) );
+  scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "qgis_locale" ), QgsApplication::locale(), true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "user_account_name" ), QgsApplication::userLoginName(), true ) );
   scope->addVariable( QgsExpressionContextScope::StaticVariable( QStringLiteral( "user_full_name" ), QgsApplication::userFullName(), true ) );