So do the French Black Copper Marans need feathers on the legs to be French?
In general yes.
Before BCMs were accepted in the American Poultry Association, people either bred to the "English standard" (clean shanks) or the "French standard" (Feathered shanks). As they were accepted into the APA with feathered shanks in their SOP, the correct name is Black Copper Marans and they are supposed to have feathered legs even they don't always have them. I breed to the feathered legs and on my website I make to note I am breeding toward the Standard of Perfection. This should tell serious breeders/buyers that they have feathered legs.