Android Text To Speech in Arabic

I want to make a TTS application trying available locales for TTS.
It doesn't work when I set it for Arabic-Egypt (available in supported locals). I miss something?

//  Working examples
Locale locale = new Locale("en", "EN");
Locale locale = new Locale("es", "ES");
result = tts.setLanguage(Locale.FRENCH);

//  It doesn't work

Locale locale = new Locale("ar", "EG");
result = tts.setLanguage(locale);