Add runtime language switching without restart.

Author: mohsenD98

src/core/appinterface.cpp

@@ -24,11 +24,15 @@
 #include "sentry_wrapper.h"
 #endif
 
+#include <QCoreApplication>
 #include <QDirIterator>
 #include <QFileInfo>
 #include <QImageReader>
+#include <QLocale>
 #include <QQuickItem>
+#include <QSettings>
 #include <QTemporaryFile>
+#include <QTranslator>
 #include <qgsapplication.h>
 #include <qgsauthmanager.h>
 #include <qgsmessagelog.h>
@@ -227,6 +231,60 @@ QVariantMap AppInterface::availableLanguages() const
   return languages;
 }
 
+void AppInterface::changeLanguage( const QString &languageCode )
+{
+  QSettings settings;
+  settings.setValue( QStringLiteral( "/customLanguage" ), languageCode );
+
+  static QTranslator qfieldTranslator;
+  static QTranslator qtTranslator;
+  static bool translatorsInitialized = false;
+
+  if ( translatorsInitialized )
+  {
+    QCoreApplication::removeTranslator( &qtTranslator );
+    QCoreApplication::removeTranslator( &qfieldTranslator );
+  }
+
+  if ( !languageCode.isEmpty() )
+  {
+    if ( !qfieldTranslator.load( QStringLiteral( "qfield_%1" ).arg( languageCode ), QStringLiteral( ":/i18n/" ), "_" ) )
+    {
+      qWarning() << "Failed to load QField translation for" << languageCode;
+    }
+    if ( !qtTranslator.load( QStringLiteral( "qt_%1" ).arg( languageCode ), QStringLiteral( ":/i18n/" ), "_" ) )
+    {
+      qWarning() << "Failed to load Qt translation for" << languageCode;
+    }
+
+    QCoreApplication::installTranslator( &qtTranslator );
+    QCoreApplication::installTranslator( &qfieldTranslator );
+    translatorsInitialized = true;
+  }
+  else
+  {
+    translatorsInitialized = false;
+  }
+
+  if ( !languageCode.isEmpty() )
+  {
+    QLocale customLocale( languageCode );
+    QLocale::setDefault( customLocale );
+    QgsApplication::setTranslation( languageCode );
+    QgsApplication::setLocale( QLocale() );
+  }
+  else
+  {
+    QLocale systemLocale = QLocale::system();
+    QLocale::setDefault( systemLocale );
+    QgsApplication::setLocale( systemLocale );
+  }
+  if ( mApp )
+  {
+    mApp->retranslate();
+  }
+}
+
 bool AppInterface::isFileExtensionSupported( const QString &filename ) const
 {
   const QFileInfo fi( filename );

src/core/appinterface.h

@@ -122,6 +122,13 @@ class AppInterface : public QObject
     //! Returns a list of available UI translation languages
     Q_INVOKABLE QVariantMap availableLanguages() const;
 
+    /**
+     * Changes the application language to the specified \a languageCode.
+     * This will reload translators and refresh all QML translations without restarting the app.
+     * \param languageCode the language code (e.g., "en", "de")
+     */
+    Q_INVOKABLE void changeLanguage( const QString &languageCode );
+
     //! Returns TRUE if a given \a filename can be opened as a project or standalone dataset.
     Q_INVOKABLE bool isFileExtensionSupported( const QString &filename ) const;
 

src/qml/QFieldSettings.qml

@@ -715,18 +715,6 @@ Page {
                 wrapMode: Text.WordWrap
               }
 
-              Label {
-                id: languageTip
-                visible: false
-
-                Layout.fillWidth: true
-                text: qsTr("To apply the selected user interface language, QField needs to completely shutdown and restart.")
-                font: Theme.tipFont
-                color: Theme.warningColor
-
-                wrapMode: Text.WordWrap
-              }
-
               QfComboBox {
                 id: languageComboBox
                 enabled: true
@@ -743,8 +731,12 @@ Page {
 
                 onCurrentIndexChanged: {
                   if (currentLanguageCode != undefined) {
-                    settings.setValue("customLanguage", languageCodes[currentIndex]);
-                    languageTip.visible = languageCodes[currentIndex] !== currentLanguageCode;
+                    var newLanguageCode = languageCodes[currentIndex];
+                    if (newLanguageCode !== currentLanguageCode) {
+                      // Change language immediately without restart
+                      iface.changeLanguage(newLanguageCode);
+                      currentLanguageCode = newLanguageCode;
+                    }
                   }
                 }
 
@@ -758,7 +750,6 @@ Page {
                   languageComboBox.model = items.concat(Object.values(languages));
                   languageComboBox.currentIndex = languageCodes.indexOf(customLanguageCode);
                   currentLanguageCode = customLanguageCode || '';
-                  languageTip.visible = false;
                 }
               }