Mandarins being wildfowl will be wild even hand reared chicks are scatty, we have ours tamed enough to be able to walk through them without them going mad but not handleable. Are yours pinioned or not, if not and let out of an enclosed pen they will fly away, In the uk it is illegal to release wildfowl into the wild either by escape or deliberately, dont know about france. ours are in a covered enclosure ( not to stop them escaping but to prevent attack from birds of prey) with pond and plenty of shrubbery so they have places to hide, shelter etc. the birds need a nest box come spring, about 18 inches off ground and about 1 ft square 2 foot tall with an opening 2/3 rds the way up the side( a hole about 3 inches in dia), the inside will need a rough surface so they can climb out and when the chicks hatch so they can climb out too, this can be grooves cut in the wood or wire or sacking. Our enclosure has a large rabbit hutch 4 ft x 2 ft x 2ft that they like to sit on and in really bad weather they go inside also use it on hot days. We do not put them away at night as doing so can stress them, and stress is the biggest killer in wildfowl.
Feeding ours are fed on a mix of growers layers and wheat and seem to thrive on it, they also have drinking water bowls in addition to the pond and have an area below the pond which we flood on a daily basis to give them a natural marsh to waddle in and root through the mud. The higher part of the ground is grass which they also root through for bugs.
Enjoy your ducks

Hi our wildfowl pen contains Mandarins in normal, silver and blonde, carolinas, laysan teal, brazilian teal, hottentot teal, fulvous whistling ducks, northern pintail, they all get on without any problems so with enough space and cover almost any wildfowl should be possible to mix in with them. We have found the teal less skittish than the other breeds from day one, but as said in previous post they have all tamed down to the point where we can walk through them without them going mad, they will even come to within inches of the food bowl when being topped up.

Have only just seen your post. My Mandies (one pair)are in a 3mtr square run with a small hut and a large water tray at night but are out in my pond area in the day that is about 50mtr x20 with a pond of approx. 30mtr x10 they are very good when we put them in their run at teatime,  we just walk quietly behind them and walk them to their run or use a rope to get them off the pond if thats where they are at the time. I would not say they were tame but as long as you are careful not to panick them they are well behaved, but if you have to catch them to worm them or anything it is just bedlam in their run and they are nervous for a day or two. They share the pond with my call ducks. I dont think Mandarins will ever be tame like like domestic ducks. A friend of mine has just given up on her Carolinas and sold them as she thought they were far too wild, she didnt realise when she got them that they would be any different from her domestic ducks