I haven't been in your situation. I have known children who only speak non-English languages who have entered my child's English speaking classes. It helps if there are a couple of "buddies" in the class who can look out for them and help them out a little. Most children like to be helpful and they feel good about being picked for this role. I would ask the teacher to find a couple of children who can be buddies. Perhaps you could arrange a couple of playdates at home too, to nuture the relationship a little.
Do you speak any Chinese (Mandarin?) at home? It will help if he is familiar with a few important words - bathroom, "I don't understand", etc. - before he goes to school. If that's not possible, perhaps you could provide him with a couple of flashcards to use, with a simple picture and the Chinese characters written out so he can use them if he's really having a problem communicating - bathroom, feeling ill, etc.
Does the school welcome parent volunteers? If so, are you able to spend a little time in the class with him, perhaps a couple of times a week?
The children adapted very quickly and learned English in an amazingly short period of time. I hope things go well with your ds too.