Preferred Language in a profile doesn't show/behave as required when so configured
I've got a multilingual CiviCRM/Drupal (5.24.6/7.x) with a profile that includes the (core) field preferred_language.
Setting it as required in the profile web interface does not mark the field as required, and also does not apply the desired functionality.
I'd guess it's something missing in this file: https://lab.civicrm.org/dev/core/-/blob/master/CRM/Core/BAO/UFGroup.php
I did a quick test on a separate Drupal 8 install and observed the same issue.
Clues or suggestions welcome.