Being from the united states i feel the most important language i can learn would be spanish. alot of people find it surprising that the united states has such a strong latin infulance. i would say within 10 years, spanish will become the second official language of the USA.
Learning a second language. Which would you learn?
I will choose to learn Spanish as well. I do speak Putong and Min Nan Hua Chinese,Thai and English. Well, Spanish is a very unique language. Unlike French,it is much more easier to learn. And the pronounciation is not so confusing. Of all European countries,i like Spain the most!!! 
First of all there is no official language of the Untied States. Secondly I would probably learn Spanish aswell.
I'm trying to choose between Spanish and Chinese at the moment.
Learn whatever language you'll be using the most - practice helps a lot. If you're in the US, Spanish would certainly be a reat choice!
I am an student of English language ( the most perferct language for me ) It is very well made language the english.
I speak Portuguese as native language, but besides English , i am liking to learn Italian, and also a bit of German. Imparando tedesco si .
I'd choose one that is likely to enable communication with people that for whatever reason are unlikely to start learning English themselves; Chinese would have my preference over Spanish.
Gotta be Spanish man, very useful next to English. German sounds ugly (no offence), French pretty but poncy and difficult and not very useful, Italian same as French.
but as we all know English is the natural language of the human being so we could all just be ignorant and carry on speaking louder and slower so that our foreign counterparts will eventually get the message...its works for generations why change it?
Well, I speak five languages fluently (three as mother tongues) -- one Latin, two Slavonic, one Germanic, and this weird mongrel -- English.
I can communicate/read/write (or in the case of Mandarin/Putonghua speak only) about 17 or 18 other ones.
I do want to improve my Portuguese, which lags behind my Italian and Spanish (French is one of my mother tongues); I love Portugal and wouldn't mind settling there at some point.
Hello TylerJames
If I was more talented with languages, than I am, I would learn a bunch of them. It would be great to know a lot of languages. It would enhance the travelling experience. When I was working in Dublin, there used to be people in the company, who were hired for their language skills. Some of them could speak 10 languages. Unfortunately, I do not have such abilities, so I learn whichever languages are the most useful to me. At the moment, I am learning German, because I live in Germany. I also took a bunch of Spanish lessons, when I was travelling in South America, becuase I studied Spanish in High School, so already knew some.
Mel