I was never sure why they were specifically French hens.
The cockerel is a symbol of France, of course (this started off as a Roman joke based on the fact that the Latin gallus means both Gaul (the Roman word for France) and cockerel).
But what is a French hen like?
I've always imagine something tremendously chic, head held high, combining true elegance, the production of exquisite eggs, and an excellent flavour.
There are certainly French breeds of hen like that:
Faverolles cockerel and hen.
but in the song of the Twelve Days of Christmas the chances seem to be that French really just means foreign: something exotic, and therefore mysterious and exciting.
So, are French things mysterious and exciting?
Well, there are 59 entries for French things in my Collins dictionary. The thing you notice first about them is that, while some of them are genuinely from France (French bulldogs, for instance), some definitely aren't (what we call French Horns have the wrong type of valves to be French Horns: they're actually specifically German horns). French chalk is a particularly pleasing example of bad labelling, being almost certainly neither from France nor made of chalk.
Sp. is it time we tidied English up so it starts making sense?
Well, apart from the fact that you'd have to get rid of half the language before you could begin to make it work, no, I don't think it is.
It would mean you'd understand what you were talking about the whole time.
But what would happen to all the mystery and excitement, then?
Word Not To Use Today Without A Bit Of Thought: French. This word comes from the Old English Frencisc, Frankish, perhaps from frankon, a lance.