Change the language on-the-fly (no restart)

src/app/main.cpp

@@ -19,6 +19,7 @@
 #include "platformutilities.h"
 #include "qfield.h"
 #include "qgismobileapp.h"
+#include "translatormanager.h"
 #if WITH_SENTRY
 #include "sentry_wrapper.h"
 #endif
@@ -188,31 +189,31 @@ int main( int argc, char **argv )
   auto sentryClose = qScopeGuard( [] { sentry_wrapper::close(); } );
 #endif
 
-  QTranslator qfieldTranslator;
-  QTranslator qtTranslator;
+  QTranslator *qfieldTranslator = TranslatorManager::instance()->qfieldTranslator();
+  QTranslator *qtTranslator = TranslatorManager::instance()->qtTranslator();
   bool qfieldTranslatorLoaded = false;
   bool qtTranslatorLoaded = false;
   if ( !customLanguage.isEmpty() )
   {
-    qfieldTranslatorLoaded = qfieldTranslator.load( QStringLiteral( "qfield_%1" ).arg( customLanguage ), QStringLiteral( ":/i18n/" ), "_" );
-    qtTranslatorLoaded = qtTranslator.load( QStringLiteral( "qt_%1" ).arg( customLanguage ), QStringLiteral( ":/i18n/" ), "_" );
+    qfieldTranslatorLoaded = qfieldTranslator->load( QStringLiteral( "qfield_%1" ).arg( customLanguage ), QStringLiteral( ":/i18n/" ), "_" );
+    qtTranslatorLoaded = qtTranslator->load( QStringLiteral( "qt_%1" ).arg( customLanguage ), QStringLiteral( ":/i18n/" ), "_" );
   }
-  dummyApp->installTranslator( &qtTranslator );
-  dummyApp->installTranslator( &qfieldTranslator );
+  dummyApp->installTranslator( qtTranslator );
+  dummyApp->installTranslator( qfieldTranslator );
 
   delete dummyApp;
 
   QtWebView::initialize();
 
   QgsApplication app( argc, argv, true, profilePath, QStringLiteral( "mobile" ) );
 
-  if ( !qfieldTranslatorLoaded || qfieldTranslator.isEmpty() )
+  if ( !qfieldTranslatorLoaded || qfieldTranslator->isEmpty() )
   {
-    ( void ) qfieldTranslator.load( QStringLiteral( "qfield_%1" ).arg( QLocale().name() ), QStringLiteral( ":/i18n/" ), "_" );
+    ( void ) qfieldTranslator->load( QStringLiteral( "qfield_%1" ).arg( QLocale().name() ), QStringLiteral( ":/i18n/" ), "_" );
   }
-  if ( !qtTranslatorLoaded || qtTranslator.isEmpty() )
+  if ( !qtTranslatorLoaded || qtTranslator->isEmpty() )
   {
-    ( void ) qtTranslator.load( QStringLiteral( "qt_%1" ).arg( QLocale().name() ), QStringLiteral( ":/i18n/" ), "_" );
+    ( void ) qtTranslator->load( QStringLiteral( "qt_%1" ).arg( QLocale().name() ), QStringLiteral( ":/i18n/" ), "_" );
   }
 
   if ( !customLanguage.isEmpty() )
@@ -354,8 +355,8 @@ int main( int argc, char **argv )
   QCoreApplication::setOrganizationDomain( "opengis.ch" );
   QCoreApplication::setApplicationName( qfield::appName );
 
-  app.installTranslator( &qtTranslator );
-  app.installTranslator( &qfieldTranslator );
+  app.installTranslator( qtTranslator );
+  app.installTranslator( qfieldTranslator );
 
   qputenv( "QT_QUICK_CONTROLS_STYLE", QByteArray( "Material" ) );
   qputenv( "QT_QUICK_CONTROLS_MATERIAL_VARIANT", QByteArray( "Dense" ) );

src/core/CMakeLists.txt

@@ -102,6 +102,7 @@ set(QFIELD_CORE_SRCS
     pluginmanager.cpp
     pluginmodel.cpp
     resourcesource.cpp
+    translatormanager.cpp
     printlayoutlistmodel.cpp
     projectinfo.cpp
     projectsource.cpp
@@ -234,6 +235,7 @@ set(QFIELD_CORE_HDRS
     pluginmanager.h
     pluginmodel.h
     resourcesource.h
+    translatormanager.h
     printlayoutlistmodel.h
     projectinfo.h
     projectsource.h

src/core/appinterface.cpp

@@ -20,15 +20,20 @@
 #include "platformutilities.h"
 #include "qfield.h"
 #include "qgismobileapp.h"
+#include "translatormanager.h"
 #if WITH_SENTRY
 #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 +232,55 @@ QVariantMap AppInterface::availableLanguages() const
   return languages;
 }
 
+void AppInterface::changeLanguage( const QString &languageCode )
+{
+  if ( !languageCode.isEmpty() && !availableLanguages().contains( languageCode ) )
+  {
+    qWarning() << "Language code" << languageCode << "is not available, ignoring language change request";
+    return;
+  }
+
+  QTranslator *qfieldTranslator = TranslatorManager::instance()->qfieldTranslator();
+  QTranslator *qtTranslator = TranslatorManager::instance()->qtTranslator();
+
+  QCoreApplication::removeTranslator( qtTranslator );
+  QCoreApplication::removeTranslator( qfieldTranslator );
+
+  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 );
+
+  QSettings settings;
+  settings.setValue( QStringLiteral( "/customLanguage" ), languageCode );
+
+  if ( !languageCode.isEmpty() )
+  {
+    QLocale customLocale( languageCode );
+    QLocale::setDefault( customLocale );
+    QgsApplication::setTranslation( languageCode );
+    QgsApplication::setLocale( QLocale() );
+  }
+  else
+  {
+    QLocale systemLocale = QLocale::system();
+    QLocale::setDefault( systemLocale );
+    QgsApplication::setTranslation( systemLocale.name() );
+    QgsApplication::setLocale( systemLocale );
+  }
+  if ( mApp )
+  {
+    mApp->retranslate();
+  }
+}
+
 bool AppInterface::isFileExtensionSupported( const QString &filename ) const
 {
   const QFileInfo fi( filename );

src/core/appinterface.h

@@ -122,6 +122,14 @@ 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")
+     * \see availableLanguages
+     */
+    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/core/translatormanager.cpp

@@ -0,0 +1,40 @@
+/***************************************************************************
+ translatormanager.cpp - TranslatorManager
+
+ ---------------------
+ begin                : June 2025
+ copyright            : (C) 2025 by Mohsen Dehghanzadeh
+ email                : [email protected]
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#include "translatormanager.h"
+
+#include <QTranslator>
+
+TranslatorManager::TranslatorManager()
+  : mQFieldTranslator( std::make_unique<QTranslator>() )
+  , mQtTranslator( std::make_unique<QTranslator>() )
+{
+}
+
+QTranslator *TranslatorManager::qfieldTranslator()
+{
+  return mQFieldTranslator.get();
+}
+
+QTranslator *TranslatorManager::qtTranslator()
+{
+  return mQtTranslator.get();
+}
+
+TranslatorManager *TranslatorManager::instance()
+{
+  static TranslatorManager *sInstance = new TranslatorManager();
+  return sInstance;
+}

src/core/translatormanager.h

@@ -0,0 +1,56 @@
+/***************************************************************************
+ translatormanager.h - TranslatorManager
+
+ ---------------------
+ begin                : June 2025
+ copyright            : (C) 2025 by Mohsen Dehghanzadeh
+ email                : [email protected]
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef TRANSLATORMANAGER_H
+#define TRANSLATORMANAGER_H
+
+#include <memory>
+
+class QTranslator;
+
+/**
+ * \brief Provides access to shared translator instances for runtime language switching.
+ *
+ * Translators are shared between startup (main.cpp) and runtime switching (AppInterface::changeLanguage).
+ * \ingroup core
+ */
+class TranslatorManager
+{
+  public:
+    //!  Constructor
+    TranslatorManager();
+
+    //! Copy constructor is deleted (singleton pattern)
+    TranslatorManager( const TranslatorManager & ) = delete;
+
+    //! Assignment operator is deleted (singleton pattern)
+    TranslatorManager &operator=( const TranslatorManager & ) = delete;
+
+    //! Returns the global QField translator instance.
+    QTranslator *qfieldTranslator();
+
+    //! Returns the global Qt framework translator instance.
+    QTranslator *qtTranslator();
+
+    //! Returns the singleton instance of TranslatorManager.
+    static TranslatorManager *instance();
+
+  private:
+    std::unique_ptr<QTranslator> mQFieldTranslator;
+    std::unique_ptr<QTranslator> mQtTranslator;
+};
+
+#endif // TRANSLATORMANAGER_H

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 +731,11 @@ Page {
 
                 onCurrentIndexChanged: {
                   if (currentLanguageCode != undefined) {
-                    settings.setValue("customLanguage", languageCodes[currentIndex]);
-                    languageTip.visible = languageCodes[currentIndex] !== currentLanguageCode;
+                    var newLanguageCode = languageCodes[currentIndex];
+                    if (newLanguageCode !== currentLanguageCode) {
+                      iface.changeLanguage(newLanguageCode);
+                      currentLanguageCode = newLanguageCode;
+                    }
                   }
                 }
 
@@ -758,12 +749,11 @@ Page {
                   languageComboBox.model = items.concat(Object.values(languages));
                   languageComboBox.currentIndex = languageCodes.indexOf(customLanguageCode);
                   currentLanguageCode = customLanguageCode || '';
-                  languageTip.visible = false;
                 }
               }
 
               Label {
-                text: qsTr("Found a missing or incomplete language? %1Join the translator community.%2").arg('<a href="https://www.transifex.com/opengisch/qfield-for-qgis/">').arg('</a>')
+                text: qsTr("Found a missing or incomplete language? %1Join the translator community.%2").arg('<a href="https://explore.transifex.com/opengisch/qfield-for-qgis/">').arg('</a>')
                 font: Theme.tipFont
                 color: Theme.secondaryTextColor
                 textFormat: Qt.RichText