why we should learn english

Engish is the standard form of communication. It's used worldwide by people who are from different countries but need to communicate with each other.

English is also seen as the business language, as for reasons mentioned above.

We study it also for the reasons we study any language-we need to have a way to articulate the things we need and desire. 

English is also used primarily on the internet-which today connects millions of people world wide.

English is used in many different countries also because curing the Colonial and Imperial Age, Britain proved to be "successful" at gaining colonies on different continents around the world.