From what I've read, it is illegal to use them for hunting in France, too. On hunting forums those who ask questions about hunting with a "lance-pierre" get soundly mocked and ridiculed, before being advised to try bow-hunting. Crossbow hunting might have been made legal recently, too. But in any case, bow-hunting requires getting a hunting licence first (i.e., training and examination for rifle or shotgun) followed by a diploma from the "federation".
Game can only be hunted with approved weapons, and the catapult is not on that list, making it illegal.
I've heard stories about (possibly apocryphal) about driving through the countryside and hitting a deer or boar, and picking it up to take home, only to be stopped by the police (broken headlights, for example), followed by a search of the car, followed by a charge for "hunting with a weapon that is not approved", the weapon in question being the car...