Cheating among the international students very common in college. What should I do?
As a student there is little you can do other than inform the instructor and maybe the administration that this is rampant. You don't need to mention names, just the fact that you observe a lot of cheating. 

The one thing you want to be assured of, however, is that your own position isn't being affected. If grading is competitive in any way this is a serious problem. But otherwise, if you earn the grades you actually get the rest of it is less your concern. 

If you were an instructor I'd have different advice as I've seen this myself. I once had a group of students who really wanted to help their friends and it got out of hand. People didn't understand that it wasn't right to help weaker students get good grades if it meant the weaker students weren't really learning anything and would suffer later. We never really had a solution other than to try to convince people that is was counterproductive. Of course, it helps if the course is run in such a way that cheating has little effect, say by minimizing exams. But that is a question for faculty and administration to deal with. 

Just make sure that the system treats you fairly and complain if it doesn't.