The International Civil Aviation Organisation has published more precisely defined minimum standards for radio telecommunications (R/T) language. ICAO has amended its Annexes 1 and 10 to clarify standards for correct aviation phraseology and to establish defined levels of competence for pilots, air traffic controllers and other R/T users. English or an agreed common language must be used, and pilots should always be able to request the use of the English language by a ground control station.

Source: Flight International