I think the big reason I want to learn another language, is so I can finally travel to other countries. I've mostly only ever traveled in the states and since I speak English, it's really all I know. I wouldn't mine learning more Spanish and maybe Japanese because I'd love to travel there one day.
Being able to speak the language of any country that you want to travel to is always going to make it very easy for you to adopt to that country whenever you travel there.
It is always very frustrating when you cannot be able to communicate simply because you have a language barrier with the people living around you.