ICAO has required that all pilots and ATCs serving international air traffic routes demonstrate level 4 English language proficiency by March 5, 2008. Here are links to some ICAO websites that provide additional information.

• ICAO FAQs on Language Proficiency Requirements

ICAO Holistic descriptors

• ICAO Language Proficiency Rating Scale: Expert, Extended and Operational Levels *  (PDF - 20 KB)
• ICAO Language Proficiency Rating Scale: Pre-operational, Elementary and Pre-elementary Levels *  (PDF - 20 KB)

* Reproduced from ICAO Documentation without any modifications