After a clean install of Polylang (v 3.3.1) on Wordpress (6.1.1 up to date), I can add any language via the 'Add a new language' button.
The error message is : impossible to add an new language.
It is impossible for me also to add a new language via polylang config panel.
How did you solve this problem ?
I finally find why : the database contained old data.
I de-install polylang
I backup my site
I install WP-Optimize and clean the database completely
I install polylang
No more error when adding a new language.