This occurs because the language already exists in your database. Or at least partly.
What did you make on your site before attempting to install Polylang? Did you attempt an import, did you try another multilingual plugin? I need to know more on what you did to guide you.
I was using Elementor’s export/import tool to move a site. It installed Polylang but didn’t do the set up of course. Any time I try to add a language (even the default) whether I use the wizard or just in the general settings, always get that error.
This is what I expected. These terms are already present in your database. That’s why you can’t add these 2 languages.
They really look like Polylang languages but are not complete. That’s why they don’t appear in the languages list.
The 1 million dollars question is how your database has been filled with these 2 terms before you started adding Polylang languages. And how 3 posts or pages could have been assigned teh English languages… I doubt your Elementor import has anything related with that.
You can delete the 2 lines in the tables wp_terms and wp_term_taxonomy. This should allow you to ad your languages normally.
Only way this happened is with Elementors tool as its the only thing I used to transfer the site from one server to another. So it did, but did it BADLY.
Thanks for the awesome support. Polylang for the win!