Background: it's normal for peasants not to be fluent in their mother tongue. They're like a search engine: if you say "explosion" you get one set of results, and if you say, "rapidly expanding volume of gas as a result of a runaway chemical reaction moving faster than the speed of sound in the local medium" you get a different set of results, because the search engines don't know what words mean. They instead have a sort of historical, Pavlovian association. Use words in the "wrong" context and they get confused and lost.
We say the language becomes "corrupted" over time because the later version is inherently less fluent than the previous version. E.g. what are social conditions? They are livingish livingranks. Livingranks are livingish? You don't fuckin' say. Come up with that on your own, did you. Using "livingranks" for "things-which-we-call-conditions" is also plain wrong. I wonder what word the Old English had for worldstate? Don't forget worldstate is two syllables, conditions three.
In a corrupt language you take longer to redundantly say words that are being used wrong. It's unquestionably decline (down-sloping).
You know how I have to say "you" because English has no second-person singular? It used to, ye prat. Almost exactly this occurred: because egalitarianism, everyone started using the royal We to signal that nobody was less valuable than anyone else and especially not less valuable than royalty, to the point where the singular "I" was completely forgotten. Peasants don't know their own tongue (trying to make them pick up a second tongue is plain mean). Then ye got some troubled peasants distinguishing between we and we-all, or we and wees, to try to remember the word I. You fuckin' dolts.
Why do Americans say "entree" entering-dish, when they refer to the main course? Because Americans are not fluent and don't know what words mean.
Over time, languages (especially lingua franca and attempted imperial lingua franca) forget their own words. If they do remember the words, they forget what they mean. That's corruption.
P.S. English peasants in particular seem proud of being non-fluent in English. If they can speak their own tongue like a broken pidgin, they're as happy as a pig in shit. French peasants, at least, seem to strive (uselessly, but with feeling) to be more fluent. Japanese peasants give face to those who are more fluent than they are, rather than mocking them like English peasants do.
Then, the English peasant, speaking an improverished pidgin, keeps accidentally absorbing pretentious (stretch-ish) bureaucratese which serves the linguistic need they suddenly find themselves with. Which bureaucratisms are then used wrong, in case you weren't sure they were foreign implants.
This is why it was very correct when for centuries scholars wrote exclusively in Latin.
Should have used Greek instead, tho. Using Latin revealed they were doing it for social reasons, not logical or scholastic ones. Exactly as accused, they did it to sound fancy and for no other reason. They were correct (co-rect; with-the_line) by accident.
Scholars need their own language. Restricting a tongue to scholars means it's restricted to high-IQ users who put real demands on the tongue, which means it corrupts very slowly if at all. Even if it does get corrupt, the professionals can fix it, unlike hapless peasants.
(You don't want to know what "professional" actually means. Save yourself the headache.)
I see no reason wealthy scholars have to use a natural language. Construct a purpose-built one and use that. Maybe some kind of lojban except un-sodomized by cross-pollination with Greek.
You want "in" on the scholarly clique? Don't make scholars write in the vulgate. Merchant-tongue simply isn't good enough. Make the scholar-tongue your native language if you want it so bad, villeins.
Scholars deserve the frustration they suffer for taking the merchant whining more seriously than the merchants themselves do. Why should we do all this work if they're not willing to do any work? They were just bitching. Should have assumed bad faith and demanded proof of good faith.