Russian

Russian is the official language of Russia. In the Pilot Leonard says that Howard can speak Russian, and in The Big Bran Hypothesis, Howard speaks a Russian sentence to Penny, who does not like it.

"Howard: Ты очень красивая девушка." "Penny: I'm sorry?" "Howard: Haven't you ever been told you're beautiful in flawless Russian?" "Penny: No, I haven't." "Howard: Get used to it." "Penny: Yeah, I probably won't."