Language property is not inherited from corresponding Account settings.
Example. Account has the following settings:
country - Netherlands,
language - Dutch. In that case,
language property of a newly created User will be taken not from Account settings, but from the
APS-Locale: header of current login session.
Software-related issue #APS-44073: "CCPv2: "Language" property of created Service User is not taken from account settings".
Contact email@example.com or TAM to trace the status of the issue.