I don't see how they could realistically and fairly impose such a rule as this. It's just a coincidence that most, if not all of the paddock converse in English (generally) - it's just more convenient that way.
Because communications with the driver now are part of the telly broadcast, it might be being required for contractual reasons with the networks.
It is not specified in the SR or the TR for F1 but that doesn't mean it isn't somewhere specified in the FIA's international sporting code. Or it could be in one of those "letters of clarification" from the FIA, like the "one move" passing rule, which has force of law but doesn't appear in either the SR or the TR.
I know Civil Aviation Authority say all Aircraft communication is in english.
ICAO regulations require English
and the local language to be spoken and understood by flight deck crews and air traffic controllers for any international flight or on any international route of flight. For domestic flights within countries where English is not the spoken language, it is not required.
Si señior!
^This German was a C student in Spanish. 
Never took Spanish - oops: señor! I mixed Spanish and Italian (which I speak) as at Ferrari 
Mixing Spanish and English is known colloquially as "Spanglish." Does this mean mixing Spanish and Italian should be called "Spitalian?"
