Google tells me that several sellers have cat doors sized for french window panes and several sellers make custom cat doors, so it sure looks like a good idea. I don't know of any one who has used any of these particular sellers or manufacturers, so I don't have any advice. Sorry! Hopefully someone else will come along with some experience.
it can be done, ck the french door real close, are they seperate paynes?
some doors are just i sheet of glass, with divders attached to the glass
loks like its seperated. but a up close inspection, will determin that
if its seperate, then the other poster, was correct. ck there sites
remove the molding around the glass,measure, the glass
and ck the other site for one that fits. there easy to install,
"Real" french doors have separate pieces of glass held together with molding. It is relatively easy to remove a single piece of glass (a plane of glass) and replace that single piece of glass with a cat-door.
However, some cheaper french doors are made of a singe piece of glass that's just covered with a grid of wood that's made to look like molding holding the parts of the door together. If you have a french door like this, you'll need to replace the entire door, or at least do a very much more complicated modification, in order to get a cat door into the french door.
So, no, you're not golden if the whole door is one piece of glass. You've got trouble if the whole door is one piece of glass.