Anyway, back to the topic.
Yes, I agree that there should be an common ground from both sides. I totally understand where two sides are coming from, how most people feel uncomfortable surrounded by people speaking different language they don't understand, and also how hard for the non speaker to speak their non-native language.
If I was the manager, I probably would sit down with each individual and talk to them, explaining how their native language might be 'offensive' for other people and make them uncomfortable, so might as well not use them. Instead of prohibit them using the language EVER, make them understand where this "unwritten rule" is comming from.
If I was the non-native speaker, of course I understand completely. As a non-native speaker myself, I always have the urge to speak my mother tongue language, but in other hand, we're in America, where people speak English, if you will.
Hey Canadians, just wondering, unless if you live in Quebec, how often do you use French? Or you don't even bother to learn it in highschool?
Just my .02 cents