Gaelic was a language that Jamie McCrimmon spoke. He once tried to speak with an Atlantean by asking, "A bheil Gàidhlig agad?", which meant, "Do you speak Gaelic?" (TV: The Underwater Menace)
The Second Doctor told Bob Hall that "TARDIS" was Gaelic for "police box" when he asked what Jamie meant by that word. (TV: The Evil of the Daleks)