As a teacher - though of a slightly different age group - if your child arrived I would be absolutely expecting, and prepared for, language issues, and would also be aware of and sensitive to the fact that other countries have different school starting ages so 'school' might be a new concept for him.
I wouldn't necessarily be particularly aware of e.g. different ages for expectations of self-care (this thread has been useful in reminding me of that) so might be less prepared for / expecting that.
Basic putting on / taking off / hanging up coat, recognising name, eating independently (either from a lunch plate or from a packed lunchbox that he can open, depending on whether taking school dinners), drinking from a water bottle with a pull up or valve spout (probably more common than open cups except in the dinner hall), and managing toileting would probably be a minimum list, with the ability to at least make a good start on getting changed for PE also a good thing. Even if he has very limited spoken English, knowing 'Please' and 'Thank you' will get him a LONG way in getting help from adults!
One thing that may be used in helping him orientate himself / give him ideas about what might be coming are picture cards showing e.g. lunch, breaktime, maths, reading. if you perhaps made a game of using picture cards now, for various things you do every day, so he could go to the table when you showed him the 'lunch' card or whatever, it might help him to get used to the concept?
Once you know what school he is going to, it may be possible to e-mail / ring them so they know what sorts of things he can already do and what he might need a hand with.