According to an article I found the other day, a knowledge of languages is required for 27% of jobs in Spain, and the language most in demand is English. So if you speak English and Spanish and would like to work in Spain, there should be plenty of jobs you could apply for.
The article, which is based on information from Infoempleo, a site where you kind find jobs in Spain, also shows that French, German, Italian and Portuguese are in demand in Spain, although to a much lesser extent than English.
The article also mentions that 28% of jobs in the Basque country require a knowledge of Basque, that 13% of jobs in Catalonia require Catalan (this seems quite a low figure given the strength of the language), and that 10% of jobs in Galicia and Valencia require knowledge of the local languages.
I don’t have stats for how many jobs in Wales require a knowledge of Welsh, but I do know that Welsh is needed for many jobs in the public sector.
That’s mostly because the avarage Spaniard speaks English bad, and I mean REALLY bad. When it comes to teaching though, it’s pretty hard to get a job as most speaking in classrooms is in… Spanish.