To obtain a commercial pilot license the International Civil Aviation Organisation states that the applicant must be able to understand English. This is a safety precaution when flying internationally as one language is needed to make sure anyone can understand anyone else whichever country or airspace the plane happens to be in. 

The same applies to all shipping communications for the same reasons, with various international bodies also making English their official language, even if none of the members are native English speaking countries. For example, you find that the Organization of the Petroleum Exporting Countries (OPEC) uses English as it’s official language as does the Shanghai Cooperation Organization (SCO) even though its members are all Eurasian countries such as China and Russia.