Add option for language auto-detection.

src/Gui/MainWindow.cpp

@@ -195,7 +195,7 @@ MainWindow::initVlmcPreferences()
     CREATE_MENU_SHORTCUT( "keyboard/importmedia", "Ctrl+I", "Import media", "Open the import window", actionImport );
     CREATE_MENU_SHORTCUT( "keyboard/renderproject", "Ctrl+R", "Render the project", "Render the project to a file", actionRender );
 
-    VLMC_CREATE_PREFERENCE_LANGUAGE( "general/VLMCLang", "en_US", "Langage", "The VLMC's UI language" );
+    VLMC_CREATE_PREFERENCE_LANGUAGE( "general/VLMCLang", "default", "Langage", "The VLMC's UI language" );
     SettingsManager::getInstance()->watchValue( "general/VLMCLang",
                                                 LanguageHelper::getInstance(),
                                                 SLOT( languageChanged( const QVariant& ) ),

src/Gui/settings/LanguageWidget.cpp

@@ -66,10 +66,15 @@ LanguageWidget::LanguageWidget( SettingValue *s, QWidget *parent /*= NULL*/ ) :
                 QLocale::languageToString( locale.language() ),
                 QLocale::countryToString( locale.country() ) ), countryCode );
     }
-    m_list->addItem( "English (UnitedStates)",    "en_US" );
+    // Add the built-in us_US locale.
+    m_list->addItem( "English (UnitedStates)", "en_US" );
 
     // Sort the combobox
     m_list->model()->sort( 0 );
+
+    // Add the system default option (auto-detection of the locale)
+    m_list->insertItem( 0, "System Locale (autodetect)", "default" );
+
     QString lang = VLMC_GET_STRING( "general/VLMCLang" );
     int idx = m_list->findData( lang );
     if ( idx != -1 )