Russian

Russian language|Russian is the official language of Russia, Belarus, Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan, Crimea, and various republics of or near Russia (recognized and unrecognized e.g. Abkhazia).

Appearances in The Big Bang Theory[]

In the "Pilot", Sheldon mentions that Howard can speak Russian.
In "The Big Bran Hypothesis" (S1E02), 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 how beautiful you are in flawless Russian?

Penny: No, I haven't.

Howard: Get used to it.

Penny: Yeah, I probably won't.

In "The Hawking Excitation" (S5E21), Howard rejects Sheldon's request to see Stephen Hawking in several lanugages, including Russian "нет" (meaning "no", pronounced as "nyet").
In "The Countdown Reflection" (S5E24), dialogs between Russian cosmonaut Dimitri Rezinov and the Mission Control are conducted in Russian language. Also, it is reconfirmed that Howard can understand Russian, as he knows something is leaking from one of Dimitri's lines in Russian.