ant be that widespread when i flew air france from london city - dublin, as far as i recal, didnt hear one french voice!
Because it was not AF but Cityjet, flying for AF
SSK,
Some safety rules come sometimes from observations and recommendations after incidents/accidents, some from Human Factor studies, and often their reason is not immediately evident to the layman.
In the case of this Safety rule it has been observed (as said in the post above) that in case of emergency, stress can cause situations where people's brains work in economy and go back to basic. It is not something an airline alone has discovered, it is in every Human Factors beginners' manual. Speaking/understanding your language or a language you are very familiar with becomes more difficult, if not impossible.
I wouldn't find it unreasonable to pick people who speak the same language as the crew instead of someone whose language skills we know nothing about.
It seems not to be an international regulation - did one country legislate for it and others followed.
I'll quote myself
Every country and airline is free to apply their own rules as long as it stricter than the EU-OPS.
In this case, for reasons definitively associated with Safety.
A pal of mine once flew on an AF flight Strasbourg-Paris and was surprised to discover that the aircraft and crew were from Monarch, and all cabin announcements were in English only.
It is quite common to hire another airline to operate a flight or several flights instead of canceling. In this case the Safety rules on board are those of the airline whose aircraft is operating the flight.