Breton is the only surviving Celtic language spoken outside the British Isles! It's spoken in Brittany in France, which is the sticky-out bit that's kind of parallel to Cornwall, and it's part of the Brythonic branch of Celtic language, along with Welsh and Cornish. It's only spoken in about half of Brittany (the west half) with much frequency, though; the other non-French language spoken on the peninsula is Gallo, which is even more endangered than Breton, and neither are recognized by the French government as regional languages because they won't acknowledge any language besides French as being officially spoken in France.

It's most similar to Cornish, but has for obvious reasons a lot of French influence, and it sounds...the best way to put it is kind of like French a bit? I'm horrible at describing sensory experiences in ways that make sense to anyone besides me, so listening to this should be some help (it's a story about a sacristan and an herb-seller, I'm not quite sure what's going on but I think they argue.)

Also crêpes and that stripy French shirt both originated in Brittany!