QTextToSpeech Set Default QLocale

In Qt 5.9.0, The QTextToSpeech class provides a convenient access to text-to-speech engines.

There is a Qt example for QTextToSpeech here.

How Can I change locale and write other language(non-english) ?

I tried this code, not working:

QLocale locale;
locale.setDefault(QLocale::Persian);
m_speech->setLocale(locale);