Latin

Latin was an ancient Earth language. Father Angelo was fluent in Latin. (TV: Tooth and Claw)

When the Cardiff Space-Time Rift fractured, mixing space and time periods, a man Andy Davidson identified as dressed as a Roman soldier and not speaking a word of English was revealed by Jack Harkness to be an actual Roman Soldier who was shouting in Latin. When Andy said the only word he could pick out was Gelligaer, Gwen Cooper noted that there was a Roman fort out at Gelligaer built around 75 AD, Jack suggested that the soldier was on his way there and when time splintered he ended up in their present. (TV: End of Days)

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. (TV: The Fires of Pompeii)