[willyt]

That would be the French national grid system, no? The UK has the ordnance survey grid which is based on the OSGB36 datum. I'm pretty sure France will have a similar national datum to create their own local grid coordinates as planning and building works needs to be done in a more accurately aligned local datum than WGS84.

[wongarsu]

For mainland France it's reasonable to assume the French national grid. But what about French Guiana in South America or Mayotte in Southern Africa (an island north of Madagascar)?

France still spans the globe, with many places treated as equals to the French mainland.