There is probably some good historic explanation for why the shared characters on these keyboard layouts have been rearranged, but in practice it's so infuriating.
Although I can create every character from these three languages from an English International keyboard, of course the preinstalled international layouts on macOS, Windows and Linux differ. And if using the layout on an English/US keyboard, likely the physical key layout (~, \, Enter) is different, too.
AZERTY amélioré sure is an improvement for the French keyboard by itself, but I'd dream of a world where we have a common compose-key keyboard for all latin-alphabet based languages.