I'd hope that on a train heading for Barcelona the conductor would be able to speak Catalan! But you'd expect multilingual staff on an international train. Not many of them in England except Eurostar and TfW, where they presumably can manage at least bilingually.A major difference is that on some high speed routes - Paris to Barcelona is one - train conductors may speak up to four languages.
In October 2022, "my" conductor was able to converse in French, English, Spanish or Italian. I thought that was excellent.
While I've no way to test it, my perception in England is that it'd be fairly rare for a guard/conductor to speak more than two languages, and many would be monolingual.

