In detail (1)
ICAO (International Civil Aviation Organization) has therefore set strict language requirements. Aeroplane and helicopter pilots must demonstrate proficiency in the language used for radiotelephony. ICAO language proficiency levels Level Description Validity Level 4 (Operational) Minimum required for radiotelephony 3 years (ICAO), 4 years (EASA) Level 5 (Extended) Advanced: expected by most airlines 6 years Level 6 (Expert) Highest level on the ICAO scale No periodic re-evaluation Radiotelephony and ATC communication Radiotelephony uses standardised phraseology: "Cleared for takeoff", "Descend flight level 280", "Roger, wilco". You must know this phraseology and apply it correctly, even under pressure.