I speak English and know moderate German. I've had some French exposure in early grade school (I didn't pay attention) and I know nothing of mandarin. My teacher says I have a thing for language acquisition and I am legally a genius. Do you think I could manage?

I'm quite sure Mandarin is the hardest and I think Russian and welsh might be in there.

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.