Communication in any field, whether it be professional or personal life, is very important. The mode of communicating should be similar other wise things can get difficult. Since English is an international language, it is easier for a person to learn it and understand it for proper communication.
Especially if the person travels a lot and is a business man, learning English for the person would be an added benefit and business can do really good if proper communication is made with the clients.All over the world, the best books are written in English. The global World Wide Web is ninety nine percent in English. So if you do not know English then you are keeping your self away from half of the world's knowledge. If you do not understand English you will not be able to even read what I have written.
Students all over the world try to take English as one of their main subjects because now trends have changed and people have realized how important it is for us to learn English in order to communicate properly.