what's the old tongue? do you mean a celtic tongue, cos you've got Irish (which gets called Gaelic, but should have the Irish qualifier. Erse would be the ancient version), Scots Gaelic, Welsh (dear to my heart)?
if so, Altan do Irish, and Capercaille, Scots songs, traditional or otherwise. most of the stuff in one of these three languages i listen to is less rock and more traditional, though.