English is the most spoken language in the world, with French coming in a close second. In fact, international communications use mostly English. In the E.U., many of the emissaries speak English as a foreign language. The number of English learners in the world is huge. It currently stands at slightly more than a billion. If you intend to travel soon, you should know that English is most likely the language you will encounter both at the airport and within the country itself.
Also, once you learn English, a huge world of information will automatically be made available to you. How? The internet is mostly in English. You can send e-mails to anyone from anywhere in the world, because they will understand English. You can chat with a myriad of users; you can buy items from web sites in English.
In addition, learning English improves your prospects for employment. This is especially so if you are searching for a job in travel, marketing and maybe translation. Speaking two or more languages gives you a great upper hand over your competitors. If the job you are searching for involves public relations like those of police (generally law enforcement) and hospital staff, then it is advisable to have a working knowledge of English. It will undoubtedly be of much help one day.
If you are the kind of person who loves to interact and meet with new people, then English will be of much use to you. This is because many of the new people that you meet most probably speak English. Imagine the doors and possibilities that will be open to you once you learn how to speak and write in this great language. You might also decide to engage in an exchange of sorts. If you are Japanese trying to understand English, you might practice with an American who is trying to master Japanese.