Teaching foreign students will make you very good at communicating effectively in the cockpit, if you care about what you're doing and want to be a good instructor.
The Chinese students are evaluated on their English before they come. Some slip through the cracks, but generally speaking they work very hard.
It can be very trying at times, not because of the language barrier but because of the cultural differences in thought processes. If you want to do more than 20 hours a month, you'll probably need to be instructing Chinese people.