Adding more pages to Montenegrin Wikipedia (in the incubator) is impossible due to the error: "You are trying to create a page without a valid ISO 639-1 or -3 code..." (screenshots)

Montenegrin language has a valid ISO 639-3 code, check [https://en.wikipedia.org/wiki/ISO_639:c here] or [https://iso639-3.sil.org/code_tables/639/data/c here]. It is completely in line with[[ https://incubator.wikimedia.org/wiki/Incubator:ISO_639 | the requirements ]].

Also, there are already 1,968 articles with wp/cnr prefix.

It is possible to edit existing pages, but not to add a new one.

On the cnr talk page, other users were complaining about being unable to create new pages (a few last posts), and this has been happening for at least a year.

To replicate

Try adding a page on https://incubator.wikimedia.org/wiki/Wp/cnr (with a new user?)

Test cases (all on Ubuntu 20.04.3)

1. FF and my usual Wiki user

2. Chrome and new Wiki account

3. Brave without login

The URL related to screenshots above: https://incubator.wikimedia.org/w/index.php?title=Wp/cnr/Vuksan_Vuksanovi%C4%87&action=submit

Related posts
https://incubator.wikimedia.org/wiki/Incubator:Administrators%27_noticeboard#Unable_to_create_Wp/cnr/_page
https://incubator.wikimedia.org/wiki/Incubator:Community_Portal#Unable_to_create_Wp/cnr/_page