The readme makes it sound very simple: "Replace bert with xphonebert"
Looking a bit closer looks like it's quite a feat to make StyleTTS2 talk in non-english languages (#28)

StyleTTS2 looks like the best approach we have right now, but only english is a killer for many as it means any app will be limited to english without prospect for other users in sight.

Some help to get this going in foreign languages would be awesome.

It appears we need to change inference code and re-train text and phonetics. Any demo/guide would be great

Alternatively re-training the current PL-Bert for other languages, though that needs a corpus and I've no idea on the cost ?
(https://github.com/yl4579/PL-BERT)