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I doubt there is such a trope on TV Tropes, or it would be easy to find.
I've also never seen an example of a work that confuses those two cultures, and any cultural stereotype I've seen of France and of Italy are distinct enough that I doubt it's common to combine the two.
If a character In-Universe gets the two cultures confused, it could be Global Ignorance.
Yeah, France and Italy aren't as easily confused as the ones that already have tropes about it, like Scotireland and Spexico.

Conflation of France and Italy, in a similar vain to Scotireland. Because both are home to good food and have generally romantic-sounding languages, so they must be the same, right?