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Everyone doesn't. French windows is the correct description in the UK.
Only foreigners from the other side of the Atlantic should call them
french doors.
When describing component parts, what do you say. E.g.
I have a set of french windows. The left window has a crack ..
OR
The left door has a crack. If you had a single side and called it
a window, people would be well confused !

Only the clueless.

But you don't need to take my word for it, just consult an English
dictionary.

Incidentally french windows don't have to be in pairs. Single examples
used to be quite common.

--
Roger Chapman