With rules like
"Joining from long final, base leg, or the middle of downwind is forbidden"
it's no wonder they disregard them! Objectively there is nothing particularly wrong with any of these, just as the OHJ is inappropriate under conditions of high traffic density.
I recently heard a French pilot coming into my local airfield (full ATC); he was told to report at some VRP which (like so many VRPs) is impossible to uniquely identify unless you happen to live there, got thoroughly confused, but eventually got in OK.
That's why I don't bother to learn the stock phrases like "downwind" in French; all that somebody has to do is ask you something or instruct you to do something, on the assumption that you know a few extra words, and you are stuffed.
I think if as many French pilots came to the UK as Brit pilots go to France, there would be havoc.
This means no flying between small local airfields in these countries (unless carrying a local language pilot/passenger) but that's a price I am willing to pay. Everybody has the right to use their own language, and IMV "foreigners" should learn that language if they want to visit.
International airfields are the exception to that, for very good reasons. Yet some places (La Rochelle being one) manage to have utterly incomprehensible English ATIS, and ask you to go to VRPs which nobody can find on the VFR chart.