French

A language Howard claims to speak.

• He wishes Penny "bonne douche" (good shower) in The Pilot.

• He tells Missy she would be "très drôle" (very funny) in The Pork Chop Indeterminacy.

• In The "Bad Fish Paradigm" he enters the apartment with the question "Qu'est-ce que 'sup" (probably intending to ask "what's up?" since "qu'est-ce que" translates to "what is").

Sheldon also seems to know at least some phrases as revealed in a dialogue with Stuart in The Hofstadter Isotope:

Stuart: OK, you can throw all the French words you want, it doesn’t make you right. Sheldon: Au contraire. (on the contrary)