You may have noticed that, currently, only the user facing sites (PMUser and PMHelpdesk) offer localized versions and the PMAdmin site is only available in English.
This is by design. An enhancement request (TF00617437) has been created detailing the feature above.
The product team will evaluate the request and this feature may become available on a future release of the product.
Please refer to this article for updates or contact support referencing the Enhancement Request ID: TF00617437.