From
ICAO:
In which languages does a licence holder need to demonstrate proficiency?
Amendment 164 to Annex 1 has introduced strengthened language proficiency requirements for flight crew members and air traffic controllers. The language proficiency requirements apply to any language used for radiotelephony communications in international operations. Therefore, pilots on international flights shall demonstrate language proficiency in either English or the language used by the station on the ground. Controllers working on stations serving designated airports and routes used by international air services shall demonstrate language proficiency in English as well as in any other language(s) used by the station on the ground.