- Pavel Chekov speaks fluent Russian. He periodically lapses into it when excited, as he did in Star Trek 3: The Search for Spock.
KIRK: I'm on my way. Sulu, continue docking procedure.
SULU (OC): Aye
CHEKOV : "Ya ne sumasshedshi! (Я не сумасшедший!)" ("I'm not crazy!")
- Uhura's first language is apparently Swahili. When her memory is erased in TOS : The Changeling, she uses it while re-learning English.
UHURA: The dog has a, The dog, sikumbuka
CHAPEL: Not Swahili,
Uhura. In English. The dog has a ball. See? B, ah, ll. Ball. Now you
UHURA: The dog has a ball.
These are both backed up in TOS: The Spectre of the Gun where each person on the bridge hears a warning in their first language.
CHEKOV: It was Russian, sir. Every word.
UHURA: No, Captain. It was Swahili.
KIRK: Interesting. Telepathy.
- Hoshi Sato appears to be bilingual in Japanese, although it's not certain whether she was raised bilingual or learned it at a later date
T'POL: Captain? May I speak with you?
HOSHI: (as Archer takes the pot of oden off the stove and starts to
help himself) That is a very complex recipe. I will not serve it till
it's just right. My family's reputation is at stake.
- Captain Picard also speaks fluent French. Given that he was brought up in France, it seems likely that he was raised bilingual:
PICARD: Incroyable! Vous etes Parisienne?
Riker is surprised that she speaks French and a little jealous that
she and Picard are hitting it off so well.
MINUET : Au fonde c'est vrai, nous sommes tous Parisienne.
PICARD : Oui, au fonde nous sommes tous Parisienne.
- Ensign Muniz (DS9 : The Ship) reverts to speaking Spanish when he suffers a serious injury.
INTERIOR - ANOTHER ANGLE as Muniz starts MUTTERING pieces of Spanish... "Lindo"... "que bonita"... "noche"... O'Brien can do nothing but keep Muniz from rocking too violently.