"Do not use foreign words in narrative to show your erudition. Phonies like to stud their conversation with foreign words. If you do that in narrative, you, the author, will sound like a phony."
-- Ayn Rand, The Art of Fiction.
Ralph Puke of the comedy team of Puke and Snot used to make fun of such phonies by using foreign words, of specifically French origin, in an attempt to seduce a female member of the audience, and catastrophically failing in the process.
I strongly suspect that Rand is also commenting on a bad habit of the late conservative author William F. Buckley, Jr. I personally found it very annoying when Buckley used a foreign word or phrase, without translating it, in the articles that he wrote for National Review. If someone is speaking to their fellow citizens then they should use the common language of their nation.
I understand that there are some Leftists who also indulge in this bad habit.