if I am not mistaken in the real secrets is not mentioned that is mandatory to speak Spanish, just that in Spain you will be endorsed only with English and in case Spanish.
In vueling, just some years ago some genius (because Spanish is not mandatory for the Spanish legislation.. Always if nothing changed) wrote on the operation manual that the languages in vueling were two, English And Spanish.
At this point , that CAA asked vueling how they could check the Spanish language proficiency of his pilots.. Since at the time there was not a single approved Spanish center approved for aviation in Spain.
And vueling started some ridiculous internal exams, later on those exams, that did not have any reason to exist had to be repeated in an approved center. It was SENASA in Madrid. (Even though they were held in the vueling offices for most of the foreign pilots by SENASA examiners)
It sounded all a macho operation that costed money and had no point.
The only level assigned to foreign pilots was 4, because no other level was assigned and the exams were still at the beginning.. So in theory they should have been repeated after some years, but nothing.