Qt: Add translation support and language setting

src/duckstation-qt/mainwindow.cpp

@@ -463,6 +463,31 @@ void MainWindow::setupAdditionalUi()
     });
   }
   updateDebugMenuGPURenderer();
+
+  const QString current_language(
+    QString::fromStdString(m_host_interface->GetStringSettingValue("Main", "Language", "")));
+  for (const std::pair<QString, QString>& it : m_host_interface->getAvailableLanguageList())
+  {
+    QAction* action = m_ui.menuSettingsLanguage->addAction(it.first);
+    action->setCheckable(true);
+    action->setChecked(it.second == current_language);
+    action->setData(it.second);
+    connect(action, &QAction::triggered, [this, action]() {
+      const QString new_language = action->data().toString();
+      m_host_interface->SetStringSettingValue("Main", "Language", new_language.toUtf8().constData());
+      QMessageBox::information(this, tr("DuckStation"),
+                               tr("Language changed. Please restart the application to apply."));
+      for (QObject* obj : m_ui.menuSettingsLanguage->children())
+      {
+        QAction* other_action = qobject_cast<QAction*>(obj);
+        if (other_action)
+        {
+          QSignalBlocker blocker(other_action);
+          action->setChecked(other_action == action);
+        }
+      }
+    });
+  }
 }
 
 void MainWindow::updateEmulationActions(bool starting, bool running)