Language & SetAllIntl parameters

[Disrupi]

First of all great great project you guys have here going!

I have an issue or missunderstanding on how -Language & -SetAllIntl parameters seem to work.
My goal is to build a ISO file which yields a device having "en-us" as OS-language but have "de-de" or preferably "de-at" for region/input-locale.
Using
New-OSDCloudTemplate -name name -Language en-us -SetAllIntl de-de
yields error 87 while building the ISO (dart v10 is installed)

It would be much appreciated!