Though I don't have experience in Spain, I am a US trained accountant working in France. There is a certain level of reciprocity of qualifications throughout the EU. While the details of reporting and taxes, forms and deadlines will take you a while to learn, chances are you can do most of it yourself once you get to Spain.

The big requirement, however, is that you will have to learn the local language. Most serious tax forms, regulations and news regarding pending legislation and rules changes are NOT available in English translation - at least not in a time frame that would be useful to you if you're working with Spanish accounts.

Here in France, there is some significant demand for accountants with "anglo-saxon" accounting and English language skills, but you need the local language first. I suspect the situation in Spain is similar. If you get the basic local language skills under your belt, you should be pretty reasonably employable while you learn the Spanish accounting rules on the job.
Cheers,
Bev