So it would make sense that words or phrases specific to civil aviation would be in English.
But the language used among aviation professionals is of little to no importance to the average passenger.
From the point of view of a European going to the, say, Caribbean, jet lag is an issue - the ICAO is not.
We had some fun with making words in one of my high school German classes. The one I remember involved a tribe of black-and-white checkered Hottentots who kept kangaroos in cages. The cages were called Schwarzweisskariertehottentotenbeutelratenkaefige.
Only when I checked my memory by going to babelfish, beutelraten translated as ‘bag-guesses’ and kangaroo is Känguruh.
Your opinion. Mine is still that he had a valid, tho small, point.
You lost a “t” over the years. The word you had in mind is “Beutelratten” (literally: bag-rats). This refers to the family Didelphidae, which includes the species Didelphis, better known as opossums.
Well, but English is the “official language” of nearly everything that’s regulated by a supranational organization. That point is moot.
Funny thing is, in trying to find an actual origin for the word/phrase, I came up with scores of hits saying that the original phrase was derived from boat lag! 
Sonow I have to wonder, where DID it come from? And if it was derived from boat lag, was boat lag really ever such a problem? Because boats travel so slow compared to aircraft, I would think that the body’s rythyms would have the time needed to acclimate?
Also, what was the phenomenon called before the advent of JET travel? When 300mph prop planes ruled the airways?
I’m kind of glad I got involved in a moot argument now, as it opens up so many more questions for me.
Thanks. Still, it looks as if Frau Daschiff got it wrong if she meant kangaroos while saying opossums.
A French person is more likely to say décalage horaire and not jet-lag.