I taught only Chinese students. The students sent over by the companies had "Good" English. Some were very good and others were awful!!! Repeated ESL classes and still didn't understand anything.
As others have said, You will hear Yes too many times.
Also flying with these students is mentally draining.Saying things 3 different ways so they would understand. After 6 hours in a plane with primary students, all I did was go home and go to sleep. Always watch them. I saw more crap happen with bad landings in Instrument and Multi.
Lots of hours is the plus. They have ground schools and ESL. I didn't have to teach those, just fly.