THE WHOLE WORLD DOESN'T SPEAK ENGLISH
Learning a foreign language opens up the door to your getting to know more people and expanding your social network. If you are studying a language such as Spanish, Portuguese, or Chinese that is spoken by a large percentage of the population, you will be literally potentially tapping into a communication network with hundreds of millions of people that was previously off limits to you. If you are studying a less popular language, just think how much more valuable you will be since there are fewer foreign speakers of it.
Also, in the world of business, communication is king. It does not matter how well you can program a computer, do accounting, or design new products: if you cannot communicate with other people, you will not find the success you deserve in the business world. Learning to communicate in a foreign language effectively increases your value as a communicator. And, many people who become proficient in a foreign language end up actually improving their skills as a communicator in their native language, as well.
Learning a foreign language makes you a better communicator overall, and it therefore makes you a more attractive employee or partner in the world of business. People who speak more than one language earn more money than those who don't. That's a fact.