For handling international traffic under ICAO rules, ATC is indeed supposed to be done in English.

But if we take a look at some of the terminology in aviation, the French words cannot be ignored. Mayday and pan-pan are from the French venez m’aider and panne.

When radio silence is required, a station might command “SEE-LONCE” but this comes from the French word for silence. Though I think this is a rarity in aviation.