Thinking about it, it could be quite a political minefield. I seem to remember Aer Lingus came under fire for dropping Irish on ex-Belfast flights, and I know I've had flights to/from Switzerland that have featured announcements in what I can only assume is Romansch.

But otherwise what do flights to/from Spain do - always in Castilian, or also in Catalan, Basque, Gallician, Valencian..? Flights from Brussels always use French and Dutch, but would flights from Antwerp do the same? But then how far do you take it? Do you hear Frisian, Scots Gaelic, Swabian, Nynorsk, Jysk, Elsässerditsch, Breton, Welsh..?