Ever try learning a second language? It's pretty tough. Your brain is "hardwired" towards one language once you reach a certain age, and it is challenging to adapt to another one.
But it's quite beneficial. Not only will you be able to communicate with new people (thus opening up new means of business, relationships and information), but it also helps your mind "grow". The challenge is perfect to help keep your mind sharp, quick and healthy.
So which to choose? There are hundreds, if not thousands, of spoken languages in the world. Some, such as Spanish, are convenient due to regional reasons. Others, such as Chinese, are profitable due to business. Still others, such as French, offer the allure of the culture it provides. Choose which is best for you.
When it comes to learning, there are different ways to go about doing it. You can take a college class, an online class, purchase a program for your computer, get a tutor, or simply learn it on your own.
I'm learning Japanese on my own. I am doing so entirely free of charge because I'm using the free resources that the internet offers. It starts off basic, learning alphabet's, grammar and vocabulary. But after that, you can learn as much as you are willing to try for ... and most of it is free!
So go ahead, find a language that interests you and learn it! You will only improve yourself by doing so.