The default buttons of a QWizard are not translated.

Back/Next/Cancel/Finish etc.

Workaround:

Explicitly set the text:

setButtonText (BackButton, QObject::tr ("Back"));
setButtonText (NextButton, QObject::tr ("Next"));
setButtonText (CancelButton, QObject::tr ("Cancel"));
setButtonText (FinishButton, QObject::tr ("Done"));
setButtonText (HelpButton, QObject::tr ("Help"));