I’ve just noticed something extra: As I said before, if I select English as a language, then “Undetermined” becomes deselected, yet the content still remains viewable. Well, I’ve just figured out why the content remains viewable: It’s because “Undetermined” for some reason gets automatically re-selected; it’s just that you can’t see that it’s happened unless you refresh the whole settings page (after saving).
I think the whole language section of the settings needs a redesign, because this is very confusing.