English has become a world language. In many former British colonies, there are many local languages, but the common language that ties everyone together is English. In the scientific field, English is the language that everyone has to learn to speak. The most important journals are all in English.
And, it becomes self enforcing: As more people learn English, it becomes a more of the official world language, and thus even more important. With the fall of the Eastern Block and its Russian standard, English really has no competition.
The biggest competitor will be Chinese because of its large speaker base. As the Chinese become more technical, they'll produce their own literature and journals. Business-wise, Chinese is already a strong contender to English, and the more Chinese firms reach out to the world for resources and markets, the more important Chinese will become.
However, there are several advantages that English has. English is a very loose and adaptable language. New words are easily added, and words shift constantly between various word forms. For example, the word text was a noun (printed text), became a verb as in I texted him a message, and back to a noun as texting. English also has an extremely large vocabulary thanks to its dual French/Anglo-Saxon heritage. There are also few verb and noun forms to congregate, so it can be an easier language to pick up.
However, English's biggest advantage is that there is no official English. English freely borrows words and phrases, and quickly adapts to the speaker. It's always fun to watch the French Academy of Language ban an English phrase that actually had French roots. In 20 years, the version of English most people will be speaking won't be the American or British version, but the Indian version of the language with quite a bit of Spanish thrown in.