Italian was a language which originated in Italy.
The Fourth Doctor and Sarah Jane Smith spoke Italian when they travelled to San Martino in 1492. (TV: The Masque of Mandragora)
The Seventh Doctor mocked the Gods of Ragnarok, saying, "La commedia è finita". (TV: The Greatest Show in the Galaxy)
One of the catchphrases of the Tenth Doctor was "Molto bene!", which was also quoted by Donna Noble. (TV: Midnight, Journey's End) On one occasion, he also added "Bellissimo!" (TV: Planet of the Ood)
Contacting a fellow Slitheen operative stationed in Naples, Glune Fex Fize Sharlaveer-Slam Slitheen exclaimed "Grazie, Napoli." (TV: Revenge of the Slitheen)