Hi Pedalbin,
I was in the same situation as you a couple of years ago and, guessing from your location, did it at the same airport (cuatro vientos ?)
There arenīt actually that many differences between Spanish Law and the UK, so if you learn the fundamentals in English and then study example questions in Spanish you should get there. Law is the hardest in another language though, it took me four attempts to get through !
You will not be allowed an English dictionary in the exams, and I donīt think it would help. They like to play on the words so literal translation wonīt be any assitance.
By the way, I believe (and I stand to be corrected) you donīt actually need a flight plan for every flight in Spain. The thing is virtually all AENA airports are controlled, so you do if you use them. Another difference is that, although you will have to study the rules of night time VFR, you will not be able to practice it.
If you need more info feel free to PM me, Iīd be happy to meet up for a beer and a chat, and give you copies of example questions if it helps, although Iīm sure your school can do the same, depending on who it is.
Good luck
