I listen to LiveATC a lot and I feel it should be made International law that English must always be used in ATC.
The reason is that speaking English only gives situational awareness for EVERYBODY
Example:
On LiveATC I heard Brazilian controllers speaking good English to foreign aircrews but then cut to Portuguese to speak to a domestic carrier.
For the foreign crews who dont speak Portuguese they have no idea whats going on. “What did he tell that other airplane, what did the other airplanes pilots respond with?”