Usually French when discussing Marans, indicates lightly feathered legs, as the French standard calls for feathered legs, and the English standard does not. I'm not sure if there are English Black Coppers though... Certainly Cuckoos and Wheatens come in clean legged and feather legged, so I suppose it could happen... I just don't recall seeing it.
Agreed. French Black Copper Marans just means Black Copper Marans with feathered legs, which to me adding the term "french" is just a sales pitch - As I've yet to ever truly see a clean legged Black Copper flock.