> For example, in the US, speaking French is considered a particular accomplishment and a sign of good breeding, much more so than with any other second language.

As an American, my impression is that French is just considered more elegant and sophisticated than other foreign languages. I wouldn't consider it anymore difficult than another language, and quite a bit easier than some (e.g. Chinese).

...But I'm not a WASP, and if anyone has opinions similar to what you describe, my bet is they'd be WASPs.

I would argue it is more recent, the French really helped to free the US from British control, gave away Lousiana and gifted the Statue of Liberty.

I think there are many reasons, including yours definitely true at least in the cultural unconscious in England. Other possibly more important reasons for Americans - whose white populations come from a wider cultural European base - includes the pre-eminence of French culture in the C17-C18th and through the C19th. Furniture, arts, music, food, wines and all sorts of things were particularly refined there, from before and especially during the courts of King Louis at Versailles through tothe golden decade in the late 19th century in Paris. Everybody who had aspirations to be cultured would speak French: it was the lingua franca after all! It was the language of diplomacy. Aristocratic Russians spoke French rather than Russian. I suspect in the Germanic states that was also this looking towards a rich and prosperous France as well, to the extent of invading it once they gaind some sort of cohesion and became a Prussian / German state in the late C19th. And remember that more white Americans come from Germanic stock than English stock, which is very readily observable in surnames and physiognomy.

I am not a historian and I'm quite happy to be corrected, but I'm suggesting these as factors.

And I think that the Dutch is at least standardized in the same way for Belgium and the Netherlands. (Het groene boekje, regarding spelling, is definitely shared).

While the french wait for our equivalent before daring to use a word ?

It’s just an english habit of bashing an idiotic gallicism, just like we find their queen concept surreal and idiotic ahah