Problem/Motivation :
Hello,
I didn't find any issue talking about my problem, so I declare it here.
I found a way to create same alias for 2 different nodes.
Steps to reproduce the issue
Install from scratch drupal 8.8.0-alpha1 (or maybe others versions of drupal core).
Enable the Language module.
Create a content type A with default language 'Not specified' or 'Not applicable'
Create a content type B with default language 'English' (or any other language of your drupal site)
Create a node A of content type A with for example '/test' as alias
Create a node B of content type B with the same alias
Drupal allows it : I have now 2 nodes with the same alias and I cannot access to my node A anymore. (even trying to access via /node/nid, beacause I'm redirected to the alias)
Proposed resolution
On the alias creation, drupal just checks if this alias isn't already taken in the current language.
I think it shoulds also checks in 'und' language.
I could purpose a patch about it but I would like have your opinions first.
Thanks,
NB: Same problem with pathauto (contrib module) but I think they use the same checks as core.