I’m assuming that this means that if you select a language, you will only be shown posts of that specified language; therefore, if you choose an uncommon language, you will see very little content (I’m assuming the most common language that is used on Lemmy, currently, is English). The warning, on its own, is rather nebulous, to me.
That depends on wether or not you keep “undefined” selected.
If you select English, and nothing else, and remove “Undefined” from your selection… Yes, you’re only going to be shown posts and comments explicitly tagged as English. If you keep “Undefined” you’ll see posts in English and posts where no language was set.
If you want to see posts tagged as “French” you also need to have “French” selected in your language list.
Wait… I can select multiple languages, simultaneously? How do I do this? I tried clicking multiple things in the language list, and it just moved the selection to that other language.
Yeah the UI is pretty bad at the moment. You can select multiple items by holding the Shift key and clicking them. I don’t know how to do it from mobile.