QT application with dinamic language (QTranslator) does not work

[ddonate]

I have a QT application and I need to change language at runtime. I am using QTranslator and .qm files. The language is loaded properly but my widgets don't show the text.

Y have 'MyClass..cpp' (inherits QMainWindow):

MyClass::MyClass()
{
   ...
   selectLanguage("en");
 
   m_pLabel = new QLabel(tr("User"));
   m_pLabel->show();
 
   ...
}
 
void MyClass::selectLanguage(QString language) {
 
   QString sTranslationFile = QString("texts_%1").arg(language);
 
   QTranslator translator;
   //translator.load(":/translations/" + sTranslationFile);
   translator.load(sTranslationFile, ":/translations/");
 
   if (qApp->installTranslator(&translator))
       qDebug() << "Ok";
 }
 
 void MyClass::changeEvent(QEvent *pEvent)
 {
     if(pEvent)
     {
         switch(pEvent->type())
         {
               case QEvent::LanguageChange:
                  retranslate();
                  break;
         }
     }
 
     QMainWindow::changeEvent(pEvent);
 }
 
 void MyClass::retranslate()
 {
     qDebug() << "retranslate";
 
     if (m_pLabel)
         m_pLabel->setText(tr("User"));
 }

MyClass::MyClass()
{
   ...
   selectLanguage("en");

   m_pLabel = new QLabel(tr("User"));
   m_pLabel->show();

   ...
}

void MyClass::selectLanguage(QString language) {

   QString sTranslationFile = QString("texts_%1").arg(language);

   QTranslator translator;
   //translator.load(":/translations/" + sTranslationFile);
   translator.load(sTranslationFile, ":/translations/");

   if (qApp->installTranslator(&translator))
       qDebug() << "Ok";
 }

 void MyClass::changeEvent(QEvent *pEvent)
 {
     if(pEvent)
     {
         switch(pEvent->type())
         {
               case QEvent::LanguageChange:
                  retranslate();
                  break;
         }
     }

     QMainWindow::changeEvent(pEvent);
 }

 void MyClass::retranslate()
 {
     qDebug() << "retranslate";

     if (m_pLabel)
         m_pLabel->setText(tr("User"));
 }

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In 'myProject.pro':

...
 QMAKE_POST_LINK = lrelease.exe myProject.pro
 ...
 RESOURCES += \
     resources/resources.qrc
 
 TRANSLATIONS += resources/translations/texts_en.ts \
                 resources/translations/texts_es.ts
 ...
 DISTFILES += \
      ...
      resources/translations/texts_en.qm \
           resources/translations/texts_es.qm
In 'resources.qrc':
 
 ...
 translations/texts_en.qm
 translations/texts_es.qm

...
 QMAKE_POST_LINK = lrelease.exe myProject.pro
 ...
 RESOURCES += \
     resources/resources.qrc

 TRANSLATIONS += resources/translations/texts_en.ts \
                 resources/translations/texts_es.ts
 ...
 DISTFILES += \
      ...
      resources/translations/texts_en.qm \
           resources/translations/texts_es.qm
In 'resources.qrc':

 ...
 translations/texts_en.qm
 translations/texts_es.qm

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In 'texts_en.ts':

<!DOCTYPE TS><TS>
 <context>
     <name>MyClass</name>
     <message>
         <source>User</source>
         <translation>UserEn</translation>
     </message>
     <message>
         <source>Group</source>
         <translation>GroupEn</translation>
     </message>
 </context>
 </TS>

<!DOCTYPE TS><TS>
 <context>
     <name>MyClass</name>
     <message>
         <source>User</source>
         <translation>UserEn</translation>
     </message>
     <message>
         <source>Group</source>
         <translation>GroupEn</translation>
     </message>
 </context>
 </TS>

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Language is loaded ("Ok" appears) and "retranslate" is called, but the label does NOT show "UserEn", but "User"...

I call 'selectLanguage("es")' after a while, but the same...

I hope somebody could help me.

Thanks in advance,

Diego

[yeye_olive]

You claim that the translations are successfully installed, but your code does not check the return value of QTranslator::load().

Anyway, the main problem is that MyClass::selectLanguage() allocates the QTranslator on the stack, which means that it is destroyed as soon as you exit the function. Qt's documentation is weak when it comes to specifying lifetime requirements, but it seems to me that the QTranslator passed to QCoreApplication::installTranslator() must live until it is removed or the QCoreApplication itself is destroyed, whichever comes first.

[ChrisW67]

The observation that installTranslator() accepts a pointer and not a "const QTranslator&" is a fairly good indicator that it does not take a copy. I agree that perhaps the doc should say that and also whether the QCoreApplication takes ownership of the QTranslator instance.

[anda_skoa]

The observation that installTranslator() accepts a pointer and not a "const QTranslator&" is a fairly good indicator that it does not take a copy.

And QTranslator being a QObject derived class, which means it cannot even be copied.

Cheers,
_