@SalixAlba: I go to https://en.wikipedia.org/wiki/Category:Languages_by_country and I see

(previous page) (next page)

at the bottom.

If that is not the case, please elaborate on an exact order of steps to reproduce. Thanks!

The problem is not in the in the normal list of sub-categories but in the expanded list of categories when using the CategoryTree extension.

Top of expanded sub-sub category. In https://en.wikipedia.org/wiki/Category:Languages

Bottom of same

note how the list here stops at Languages of Tajikistan, and there is no indication that there are more entries or that the list is clipped.

Ah, thanks for explaining! In the future, when filing tasks, please include a clear list of steps to reproduce, to avoid misunderstandings:

Steps to reproduce:

1. Go to https://en.wikipedia.org/wiki/Category:Languages
2. Click on the Languages by country‎ (229 C) link itself and get redirected to that page
3. See that at the bottom of the page, there are (previous page) (next page) links
4. Go back to https://en.wikipedia.org/wiki/Category:Languages
5. Click on the small triangle in front of Languages by country‎ (229 C) to expand that entry

Expected outcome:
A full list of results, or some hint that the list is not complete.

Actual outcome:
The expanded list ends with Languages of Tajikistan‎ and is not complete.