Welsh is a Celtic language akin to Gaelic and Breton, and the extinct Manx and Cornish.

How exactly are we defining the extinction of a language? Is it extinct when the last native speaker dies? There are still people (strange, strange people) who speak Cornish, although not as a mother tongue. My great-grandmother (d. 1950ish) used many a Cornish phrase in her speech (see below). Would the dodo still be extinct if we recreated it from DNA?

Do we be off wit' yer daft nanny. Translated into Aussie as "Gee you talk a lot of s**t".