These two Jewish men are sitting in a wonderful deli frequented almost exclusively by Jews in the Jewish section of town.
They are talking amongst themselves in Yiddish. A Chinese waiter comes up and in fluent impeccable Yiddish asks them if everything is okay, can he get them anything, and so forth.
The Jewish men are dumbfounded. "My God, where did he learn such perfect Yiddish?" they both think. After they pay the bill they ask the manager of the store, an old friend also fluent in Yiddish, "Where did our waiter learn such fabulous Yiddish?"
The owner looks around and leans in so no one else will hear and says, "Shhhh. He thinks we're teaching him English."