It is not even the most commonly used language on the planet. It is barely even the most commonly used language in Texas. Many of our own MARSupials don't speak English as their native language. If the ETs picked up Earth language from monitoring Earth, wouldn't they have tried to communicate using Chinese first. I think that they have somehow monitored the communications of the probes, which are in English, and then using their knowledge of Earth used English to communicate with Enoch.
Taz