Besides my (I think..) beautifull language, I assume english is the key.
The main problem doesn´t come from professional IFR pilots, rather than from VFR newbies, with whom we have to deal everyday.
ESARR5 takes care of this, and all of us, the sooner, the better, will have to show up with good english languages skills, that will also be tested from time to time.
But till that time, I would like to point out that a whole lot of your security depends upon a controller ability to communicate. I think it is better that the controller finds himself more secure talking to spanish pilots on our own language, rather that spending time on repeating instructions.
Plus, many airport workers monitor our frequencies, in order to know, for instance, which plane is cleared to land, so they can move the buses to pick up the passengers, or select a park place. Not to talk about emergency situations, where seconds of translation may cause bigger problems. Forcing all this people to understand english fluently may take our ATS providers months of teaching.
I know foreign planes are very common in Spain, and they should be used to this, but relieving this not so well instructed task force from the foreign languages problems allows them I little rest.
Anyway, why don´t you also try to learn some spanish phraseology?. At the end, there are not so many words.
Take care too.
Á.