What is interesting is that in Mexico and parts of South America, the
controllers speak Spanish with local (or domestic) flights, and
english with international flights.
KB.


This matches with what I experienced recently. I was on the ground
aboard a United passenger flight from Brazil to the USA and listening
to the onboard channel 9 ATC to kill time. Except for the United and a
Lufthansa pilot also awaiting clearance to taxi, every other pilot was
talking Portuguese. The controllers spoke perfect ATC English but
switched to Portuguese for the local pilots. I was thinking this could
easily lead to a lack of situational awareness in a large airport like
Sao Paulo's. It was interesting that even at the local Brazilian FBO,
there was no CFI who spoke English even though the Brazilian
requirements include a proficiency requirement in English!