the likelihood an american foreign service employee would ever need to use a celtic language is not very high. similar probably holds for basque which i hear is not the easiest to learn either.
In fact, if you check the map, there's a gray spot on the north of Spain/South of France. That's Euskadi (Basque Country area).
[1] https://www.reddit.com/r/MapPorn/comments/7dith2/language_di...