On the Lemmy settings page, there is a Languages option with a warning that says:
Warning: If you deselect Undetermined, you will not see most content.
However, as you can see from the picture, I do not have any option besides English: 
Is there a way to add Languages to this list? Am I missing most content, like the warning suggests?
As @erre@feddit.win said, you have to ask the admin to allow undetermined or change your instance.
Thanks. I’ve done so.