Cultish (by Amanda Montell) is great. It also defines really well how Claude speaks currently---avant la lettre, of course. Language is a big part of the book: one example is how Scientologists can recognize each other in the wild from the language they have unknowingly adopted even for everyday conversations.
As a non-French speaker, I had assumed a native speaker would suspect that this was another instance of English taking something from French and mangling it into something worse.
You could say e.g. Spinoza was a punk avant-la-lettre, he was a punk before the word "punk" even existed. I think GP is using it exactly opposite to the normal usage.
If you really must have a counterexample, though I am afraid it will not reach you given your apparent stance about the other people, when I read Shakespeare I am constantly thinking of poetic ways to translate sentences and paragraphs into my native language (which, for the record, I consider to be great fun), yet Claude has been delivering the gibberish with increasing velocity, yes, even to me.
That said, I must confess that I have not been complaining per se—I assumed that Claude was getting better and better at mimicking the idiosyncrasies of Silicon Valley bro-speak. Judging from other comments, this may not seem to be the case after all.
It's a specific dialect of its own that comes from RL. Nobody on Earth talks about load-bearing honest caveat seams.
(Another strange thing about Opus 5 is that it will constantly re-mention things it thinks are important, probably a strategy to avoid losing them in the context history.)
