For certain languages with a non-Roman alphabet, such as Arabic, Mandarin or Hindi, the uroman 
perl package is required to pre-process the text inputs to the Roman alphabet.
You can check whether you require the uroman package for your language by inspecting the is_uroman attribute of 
the pre-trained tokenizer:
thon
from transformers import VitsTokenizer
tokenizer = VitsTokenizer.from_pretrained("facebook/mms-tts-eng")
print(tokenizer.is_uroman)