Most small (110g, 225g) gas cartridges now use EAN417 threads with a valve.
Research on this forum suggests that in France, the CampingGaz standard is preferred and that, allegedly, isn't EAN417.
So, is this true?
CampingGaz cartridges are incompatible with threaded cartridges, as the former use a kind of snap-on valve mechanism and don't have threads. Because of this, you can't use CampingGaz cartridges with threaded stoves (and vice-versa).
However, if you travel to France and have to buy cartridges there, Edelrid (and potentially other manufacturers) makes an adapter that allows you to use threaded stoves with CampingGaz cartridges. If you want to see it in action, this video nicely shows it in operation.