I like the "good" parts of most cultures that I'm aware of (I tendto conflate a lot and obviously what's "good" is subjective, it's mostly based around food and language in my case, I should have been a linguist, and there are some festivals and traditions that are nice) and there are some bits that I think should definitely be consigned to history.
I'm kind of very anti-homogenisation for pretty much the reasons you cited and also irrationally anti imperialism and colonialism so I could only accept a conlang as an auxiliary.
The "common tongue" in fantasy books.
But it is interesting to think that it might not matter what people speak, it will all be translated into what is common for the listener.
That common tongue seems to be English right now which I hate (and would have hated equally if it was any other natlang, and it also is likely to be different in other areas, it's just how it appears from where I'm standing and I am kinda short).
That's how it rolls in my head universe although apparently even they (or at least the characters I've encountered) find it easier to just learn whatever is being spoken if they're spending a decent amount of time in the area XD
Learning language isn't for everyone it seems. Some really are much, much better at it than others. It is similar to math or music I guess.
Yeh it's one of those things that anyone (bar physical/mental shenanigans) can do and not everyone can be good at (but hard work will beat lazy talent any day and hard working talent is kind of at unfair advantages XD) and probably a lot of people are put off by the sheer volume of effort it takes to be mediocre.