As a noob this is likely me, but I tried to start a community on another server and I can’t see the post (my other account used to make said community) made and set as english. Unless it’s just me being a noob, that can’t be good. A cursory look seems to confirm that I can’t see anything aside from “Undetermined”.
As far as I can tell, it’s recommended, since you otherwise don’t see posts made in other language settings, including those that are Undetermined.
There are probably some communities that were made without a fixed language setting, or were created before it, that don’t have a language marked, and as such, if you don’t pick “Undetermined”, it may not be possible to see those posts.