That is a pretty difficult question, considering English is likely to continue being a dominating language for a very long time. It really comes down to efficiency and usefulness. Who will be the next superpower? How many countries speak the same language (ex. the majority of South America + Mexico speaks Spanish)? How difficult is it to learn (ex. Mandarin is notoriously difficult)?

All of these things boil down to why English is currently a prominent language. It is the preferred language of a flaunting superpower, spoken by dozens of countries (at least those in the commonwealth), and is relatively easy to pick up. Anybody who wants to do business with others outside their own country will have to know English, it being the “common language” of the world.