I thought the underlying joke was that the French would never allow German to become the lingua franca of the EU. At the time we joined the Common Market (remember that?) I was a guest at a lunch in Paris where an eminent French professor was insisting that French absolutely had to be the dominant language because of its precision, history, beauty, etc. - and certainly never English.
I requested a right of reply, which was granted, and pointed out, with a reference to a 16th century French learned work, that since the only people who spoke French comme il faut were the French themselves, it could only be ruined if it became the common language. Whereas English, I pointed out, was a grammatical mess misspoken by the English themselves, and we wouldn’t even notice what a mess the other Europeans might make of it. I was applauded by my jolly post-prandial audience, one of whom congratulated me on my imperfect subjunctives. They’ll never let German take over!