I Still don't understand language setting in lemmy

I have both Undetermined and English in my account setting but each post and comment have those two options but i leave those it on "Select language"

Ideally i would want my posts and comments to be visible as many people as possible, hence why i selected Undetermined along since English on the assumption that most English users have Undetermined as their default

How does everyone else do it? Do you bother to select language setting for posts and comments?

Also, right now this post language setting is "Select language"