I find it rather jarring that it's insisted that Common isn't English and that languages aren't really their representations despite the evidence in front of your eyes suggesting otherwise, especially when you get into language-centric RP. For example, people use wordplay or confuse homonyms in ways that simply don't make sense if the language isn't English (or whatever). One recent instance is that a character confused the ball in Port with a ball game. There's really no other way that makes sense as it's a quirk unique to English. In language RP, people are going to notice that words like dame, madame, doamnă, domina, etc all sound like they are variants of the same etymon. Either people have to ignore these things staring them in the face, or they have to abandon details, which takes a lot of fun out of language RP.
There's also the fact that the structure and features of a language are inextricably tied to its history and affect what people do with said language. English turned out the way it did because of the way Anglo-Saxon interacted with Brythonic/Old Norse/Norman French/etc, followed by England's history of mercantilism and colonialism. The historical changes to English shifted how people wrote literature. Rhyming, for example, makes little sense in languages without the right kind of syllable structure. In Chinese languages, it is so easy for words to accidentally rhyme that Chinese literary tradition places much stricter rules on what is considered rhyming, formalized via rime dictionaries that adhere to archaic pronunciations. In Japanese, there being at most 5 x 2 ways that a word-final syllable can end, rhyming is so trivial that it's essentially nonexistent. These examples are meant to illustrate that language is a complicated thing that resists the simplistic fantasy cliché of slapping on often-butchered real-world representations while claiming that they're only there for flavour. Not to mention it really is quite insulting for people of those cultures to have their languages appropriated to provide a veneer of exoticism.
There's the drastic option of just avoiding the gratuitous use of 'flavour' real-life language representations and ruling that Common and English are the same thing, but that's just not possible at this point.
Like I've said to people on Discord, people will always have different opinions on how to handle languages. What I would like to see is a non-disruptive approach to this contention that some people have -- i.e. to keep things lax and inclusive and let everyone do as they always have, within reason. The language system is by design extensible, so people who feel that strongly about keeping languages unintelligible to others are free to populate a separate tag. They should also be free to RP that their characters either cannot understand or will not bother to make an effort to understand languages that other players have assumed or DMs have ruled to be mutually intelligible. Unless people get OOC disruptive in insisting that they must understand your language, or that you must understand theirs, I don't see a compelling reason to insist on DMs putting down their foot or players trying to police other players.