It's _your team_, the people you most closely work with every day. You shouldn't need a manager to talk to each other. Just bring it up while grabbing lunch: "

It's _your team_, the people you most closely work with every day. You shouldn't need a manager to talk to each other. Just bring it up while grabbing lunch: "hey you guys, I hear a lot of Chinese and I feel left out, and others might too". If they're half decent people they will remember this next time and stick to English.