Awwww.... C'mon.... Simple logic dictates that a teacher that cannot communicate effectively with the students cannot effectively teach any of them. The same applies the other way, a student that cannot effectively communicate with their teacher can't learn what they need to know, (assuming the teacher is competent in the subject and a competent teacher).

This is a silly subject really.... In each individual institution there needs to be the "accepted" language of teaching/learning. Both the teacher and the student _must_ be fluent in the accepted language. If the teacher isn't fluent then they should be let go.... If the student isn't fluent then they must either become sufficiently fluent to pass the course or, have a translation service available to translate both ways that is sufficient for them to pass... Bearing in mind you can't bring a "proxy" into your finals that will mean that non-native speakers would be at a disadvantage.... But, at the same time, they will have professional qualifications in your country without the ability to understand the 'finer" points of you situation..... Would you want that person as your doctor or lawyer?