Latin
From Tardis Wiki, the free Doctor Who reference
Latin was an ancient Earth language. Father Angelo was fluent in Latin. (DW: Tooth and Claw) When the Tenth Doctor and English-speaking Donna Noble arrived in Pompeii, Donna wondered what would happen if she spoke Latin to the locals, whose native language was Latin. Instead of hearing Latin, at least one native speaker of Latin believed her to be Celtic. (DW: The Fires of Pompeii)
