Question

I redefined QApplication class and add switchLanguage slot and i want to switch language when i press but1. main_ru.qm and main_de.qm is normal, 100% working. But language don’t change when i press button

// main.cpp
#include <QtGui>
#include "qmyapp.h"

int main( int argc, char** argv )
{
    QMyApp app( argc, argv );
    QTranslator translator;
    // задаём файл перевода и директорию
    translator.load( "main_ru.qm", "." );
    app.installTranslator( &translator );
    QWidget wgt;
    QLabel *lbl = new QLabel( QObject::tr( "Hello" ) );
    QPushButton *but1 = new QPushButton( "1" );    
    QVBoxLayout *vbox = new QVBoxLayout;
    QObject::connect( but1, SIGNAL( clicked() ), &app, SLOT( switchLanguage() ) );    
    vbox->addWidget( lbl );
    vbox->addWidget( but1 );
    wgt.setLayout( vbox );
    wgt.show();
    return app.exec();
}

// qmyapp.h
#ifndef QMYAPP_H
#define QMYAPP_H

#include <QApplication>
#include <QtGui>

class QMyApp : public QApplication
{
    Q_OBJECT
public:
    QMyApp(int &argc, char **argv ) : QApplication ( argc, argv ) {}
public slots:
    void switchLanguage( )
    {
        QTranslator* translator = new QTranslator();
        translator->load( "main_de.qm", "." );
        this->installTranslator( translator );
    }
};

#endif // QMYAPP_H

Answer 1

You need to call translate again after installing new translations. So after you call switchLangauge() you need to call QObject::tr() once again in whatever context it was used before.