I am an ESL teacher. His inability to follow instructions, etc ABSOLUTELY could be related to his language history. Do you notice that he has difficulty "intaking" language (such as reading or listening) or is it more difficult to output language (such as writing or speaking)? Many times these pairs go hand in hand. He may not have had a lot of opportunity to take in language in the first 3 years of his life (evident by his lower level of speaking his native language). This puts him at a disadvantage already, and then add to that his learning English. He wouldn't be a good candidate necessarily for ESL right now because he probably knows "too much" ENglish to be put in the class. I would suggest a highly trained ESL tutor who can begin to go over the basics with him. Obviously he will not catch up right away. GIve him as many verbal opportunities as possible and DON'T correct his errors as he's talking. Reading also does wonders for vocabulary. As far as ADD goes, it wouldn't hurt to have him tested, in addition to doing a learning disability test. He may have a deficiency in comprehension that would indicate a slight LD- and maybe he has been compensating so you wouldn't have noticed.
Good luck and I hope someone is able to help you
. Be patient- he needs your support
.