"It's all Greek to me" was used by Shakespear, so it is not particularly American.
We use the same words (translated in French) when we don't understand something. I find it very funny.... because I teach Greek (ancient Greek)!
We think French cooking the best food in the world, so much so, we add the word "French" in front of foods that may, or may not, have originated in France just to make it sound more exotic and fancy (French Fries, French Dressing, French Toast).
I don't know what is "French Dressing"....
I never went to the US, but a few years ago, I went to Australia and, in the restaurant of my hotel, for breakfast, I saw something called "French Toast". I didn't know what it was and I immediately wanted to taste it. It's something that in France we call "pain perdu": something you eat at home when you don't want to waste old pieces of bread! Not something fancy.
So, 10 years ago, you couldn't find it in a restaurant. Now, I think you can.... for tourists!
And you know, Americans sometimes use French words in their language: for example "déjà vu". And I'm sure I've seen other ones, on these boards.
