A complete guide to implementing language switching for Qt

button->setText(tr("Submit"));

TRANSLATIONS = translations/myapp_zh_CN.ts \
              translations/myapp_en_US.ts

#ifndef LANGUAGEMANAGER_H
#define LANGUAGEMANAGER_H
 
#include <QObject>
#include <QTranslator>
#include <QMap>
 
class LanguageManager : public QObject
{
    Q_OBJECT
public:
    static LanguageManager* instance();
    
    // List of available languages    QMap<QString, QString> availableLanguages() const;
    
    // Set the current language    void setCurrentLanguage(const QString& languageCode);
    
    // Get the current language    QString currentLanguage() const;
 
signals:
    // Language changes signal    void languageChanged();
 
protected:
    explicit LanguageManager(QObject *parent = nullptr);
 
private:
    void loadTranslations();
    
    static LanguageManager* m_instance;
    QTranslator* m_appTranslator;
    QTranslator* m_qtTranslator;
    QString m_currentLanguage;
    QMap<QString, QString> m_languages; // <code, displayName>
};
 
#endif // LANGUAGEMANAGER_H

#include ""
#include <QApplication>
#include <QDir>
#include <QDebug>
#include <QLibraryInfo>
#include <QSettings>
 
LanguageManager* LanguageManager::m_instance = nullptr;
 
LanguageManager::LanguageManager(QObject *parent) : QObject(parent)
{
    m_appTranslator = new QTranslator(this);
    m_qtTranslator = new QTranslator(this);
    
    // Initialize available languages    m_languages = {
        {"en_US", "English"},
        {"zh_CN", "Simplified Chinese"},
        {"ja_JP", "Japanese"}
    };
    
    loadTranslations();
}
 
LanguageManager* LanguageManager::instance()
{
    if (!m_instance) {
        m_instance = new LanguageManager(qApp);
    }
    return m_instance;
}
 
QMap<QString, QString> LanguageManager::availableLanguages() const
{
    return m_languages;
}
 
void LanguageManager::setCurrentLanguage(const QString &languageCode)
{
    if (!m_languages.contains(languageCode) || m_currentLanguage == languageCode) {
        return;
    }
    
    // Load the application translation    bool loadSuccess = m_appTranslator->load(QString(":/translations/myapp_%").arg(languageCode));
    
    if (loadSuccess) {
        QApplication::installTranslator(m_appTranslator);
        
        // Load the Qt basic library translation        if (m_qtTranslator->load(QString("qt_%1").arg(languageCode), 
                               QLibraryInfo::location(QLibraryInfo::TranslationsPath))) {
            QApplication::installTranslator(m_qtTranslator);
        }
        
        m_currentLanguage = languageCode;
        
        // Save to settings        QSettings settings;
        ("Language", languageCode);
        
        emit languageChanged();
    } else {
        qWarning() << "Failed to load translation for" << languageCode;
    }
}
 
QString LanguageManager::currentLanguage() const
{
    return m_currentLanguage;
}
 
void LanguageManager::loadTranslations()
{
    QSettings settings;
    QString lang = ("Language", QLocale::system().name()).toString();
    
    // If the set language is not available, use the system language or default English    if (!m_languages.contains(lang)) {
        lang = m_languages.contains(QLocale::system().name()) ? 
               QLocale::system().name() : "en_US";
    }
    
    setCurrentLanguage(lang);
}

// 
#include <QMainWindow>
#include ""
 
namespace Ui {
class MainWindow;
}
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
 
public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
 
protected:
    void changeEvent(QEvent *e) override;
 
private slots:
    void onLanguageChanged();
    void on_actionChinese_triggered();
    void on_actionEnglish_triggered();
 
private:
    Ui::MainWindow *ui;
    void updateUI();
};
 
// 
#include ""
#include "ui_MainWindow.h"
 
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    
    // Connect language to change signal    connect(LanguageManager::instance(), &LanguageManager::languageChanged,
            this, &MainWindow::onLanguageChanged);
    
    updateUI();
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::changeEvent(QEvent *e)
{
    QMainWindow::changeEvent(e);
    if (e->type() == QEvent::LanguageChange) {
        ui->retranslateUi(this);
        updateUI();
    }
}
 
void MainWindow::onLanguageChanged()
{
    // Handling after language changes    updateUI();
}
 
void MainWindow::updateUI()
{
    // Update text in non-UI files    setWindowTitle(tr("Multilingual Application"));
    statusBar()->showMessage(tr("Current language: %1")
                            .arg(LanguageManager::instance()->currentLanguage()));
}
 
void MainWindow::on_actionChinese_triggered()
{
    LanguageManager::instance()->setCurrentLanguage("zh_CN");
}
 
void MainWindow::on_actionEnglish_triggered()
{
    LanguageManager::instance()->setCurrentLanguage("en_US");
}

#include <QApplication>
#include ""
#include ""
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    
    // Initialize the language manager    LanguageManager::instance()->>setCurrentLanguage("zh_CN");
    
    MainWindow w;
    ();
    
    return ();
}

lupdate   # Generate .ts filelinguist translations/myapp_zh_CN.ts  # Use Qt Linguist to translatelrelease   # Generate .qm file

<RCC>
    <qresource prefix="/">
        <file>translations/myapp_zh_CN.qm</file>
        <file>translations/myapp_en_US.qm</file>
    </qresource>
</RCC>