

Subscribe to all of them. It won’t be a problem.
It’s like if you followed #s of the same thing on Instagram, twitter, mastodon, bluesky, and whatever the equivalent of # is on Facebook, then a reddit sub with the same name. Different populations and user bases, but that’s a good thing.
There’s some degree of consolidation that happens, particularly when one community is on a bigger instance and would be better served by being hosted elsewhere. But there’s not really any barriers to using multiple. If you crosspost, you have better chances of it being seen anyway, and you’ll get access to any responses. If you’re wanting to comment, then the OP that crossposted is going to get your response no matter which ones it’s in.
Only drawback is that your comment in one won’t show in the others unless you copy/paste it. Which is perfectly valid if you want to, but most people would see your comment eventually anyway, so the conversation will still happen if it would have in the first place.
I kinda had issues adapting to it myself, but now I tend to prefer it when communities are spread out, because every instance has its own vibe usually. So you get different kinds of discussions than you would if there was only one community on one instance.
Some subjects end up needing a single community just to make it easier to find, but it’s pretty rare imo.
Formality and standardized grammar.
At some point, when you’re involving teaching a language to a class, you need a systematic way of doing so.
Typically, that means going with dictionaries and that in turn is likely to be the most formal version of a language’s pronunciation. And, with grammar, you start with the simplest but also most standardized, codified version because that’s what the books are going to use.
You don’t worry about idiom and dialect until you’ve got a fairly good grasp of the formal. Since Castilian Spanish is more or less the oldest formal Spanish, we end up learning that first.
Like, I suck at learning languages. But I tried several. One of those was Spanish. School Spanish is kinda like school English, it’s taught in strict way. Vocabulary with pronunciation, grammar rules, verb conjugation. Conversationsal Spanish just isn’t what most schools are going to start with. One could argue whether or not that’s the best place to start or not, but it is the way most languages get taught.
I dated a girl from Mexico City during that time, and she said the books were essentially the same there at least.