Nepali is not a language supported by the Google Text To Speech (TTS) engine. MIT does not create languages for the TTS. As far as I can tell, you cannot use AI2 for the Nepalese language TTS.
Edit: this is an updated list : Bengali (Bangladesh), Cantonese (Hong Kong), Chinese (China), Chinese (Taiwan) Danish, Dutch, English (Australia), English (India), English (United Kingdom), English (United States), Finnish, French, German, Hindi, Hungarian, Indonesian, Italian, Japanese, Korean, Norwegian, Polish, Portuguese (Brazil), Russian, Spanish (Mexico), Spanish (Spain), Spanish (United States), Swedish, Thai, Turkish, and Vietnamese.
Regards,
Steve