I teach in a large school in Miami. Our high school is over 60% hispanic. We also have a growing Asian population. There are quite a few students who speak little or no English. Don't let this bother you. A good student is a good student no matter what language they speak. I have taught AP computer science and AP Calculus since the mid '80's and have had good results with these students. They can usually find a way to work around language barriers.