If, during Language Pack installation, you receive errors related to "SystemSettingsAdminFlows.exe", please note the following resolution. Also, if you are looking to implement a UI language other than the default of English, continue reading.
A local administrator account is required to perform a language pack installation. You can create one on the server template itself, and then log into it.
You can then follow this guide (all BUT the sysprep actions, see important note below) to install the language pack. Once installed, you can return to your domain administrator account to set the preferred display language and copy it to New user accounts.
You should NOT be applying the language pack system-wide (this means it would be applying at boot, and even the boot-up screens would be in that language), since Nerdio partners have found this will break the required Azure agents at some point during the image creation process. Therefore, we can only apply the language packs at user level at this time.
The Important Note: Do NOT proceed with the manual sysprep actions listed in the above Microsoft article. Nerdio technology conveniently completes those required steps for you when you use the "Power off and set as image" and the Add or Update hosts options.