Granted, the warning says clearly “If you deselect Undetermined, you will not see most content”, which places the onus on the individual user, as apposed to logic built into Lemmy on which posts/comments can be viewed, while also leaving it to each user to have to weed out alternate languages for their views which are incorrectly set. This is indeed leading to many posts simply not appearing (as designed and intended), which is less than ideal when trying to grow a user base/community.
I think it would work fine if we could set a default language in our profile, so that we didn’t have to select it manually every time we made a post.