Breton is not thought to be a modern-day descendant of any continental Celtic language such as Gaulish, though evidently it has borrowed some features from it, but it is rather descended from insular Brythonic. The other local language (Gallo) derives from Latin.
It is spoken by people whose ancestors fled southwest Britain at the time of the Saxon invasions of that country. As such, it has much in common with Cornish and to a slightly lesser extent Welsh, although there are vocabulary and spelling differences owing to the influence of French upon the language.
Although most Bretons no longer speak Breton, an effort has been underway for several years to begin teaching the language in schools to keep it alive.