Which language should I learn…?

Basically, I need to do a language at GCSE level because my school doesn't offer it and on the course I want to apply for, it's almost vital you have a GCSE in any language.

So, what should I learn? I'm thinking of only learning enough to get to C-B level, how long should that take? Suggest anything really, most stuff is available at GCSE and I'll be taking it as an External Candidate via self-study.

I'm always wanted to learn Welsh, but I have no real reason for doing so, I'm not Welsh and I don't even live in Wales. Oh well, I'd rather learn Welsh over Polish or Urdu anyday.

Thanks for any suggestions.

Also, are there any languages that are easier at GCSE level than others?

I am keen to learn a foreign language (preferably more in future) and as I am a fast learner and not too dull, I think I'll be able to study it no matter how complex it is in terms of grammar/script/etc.

So why not learn something that will be useful?

Mandarin is one of the most spoken languages in the world but will it be needed in future? I'm planning on studying medical science, by the way. I was wondering about Spanish since there are a lot of countries that use it. What about French, Italian and Portuguese? Are they widespread?

I'm acquainted with English (duh!), Sanskrit, Hindi, Urdu and some regional languages, too.

So what do you think? Which language(s) would be most useful?

By the way, I won't be having much problem learning any kind of language... except something spoken by a small number like Zulu, Welsh or something like that, for which the books and classes aren't easily available.