This is due to the local Administrator Group being called "Administrateur" instead of "Administrators".
If you create a new Local Group called Administrators and add the Users to that Group then they're able to log in.
It seems that if the Local Admin Group is any different language Password Manager can't see it correctly.
The following Enhancement Request has been created to possibly fix this issue in a future release of Password Manager:
ER 121839: Ability to support Password Manager if the Local Admin Group is any different Language.