Answer:
English is the highest spoken language, about 20% of the entire population speaks it. Second is Mandarine Chinese coming in at about 14%. Depending on where you are located it is best to learn the native language.
A benefit of learning English is that you could meet different people who speak the language and gain more knowledge and social abilities. Another way you could benefit is it gives you a better look at hobbies such as reading, maybe you find a book in English but you can't read it because you don't know English, well because your learning English you can read that book.
I hope this helped!