How to change System Language with Powershell - powershell

Question

I have a PowerShell script that intends to change the System Locale on a Windows 10 Machine, but it doesn't really change that much, it just "downloads" the language but doesn't set it to the language, so I have to do it manually.
Set-Culture de-DE
Set-WinSystemLocale -SystemLocale de-DE
Set-WinUILanguageOverride -Language de-DE
Set-WinHomeLocation -GeoId 94
New-WinUserLanguageList -Language de-DE
Set-WinUserLanguageList de-DE -Force
shutdown -r;exit
It outputs this
LanguageTag : de-DE
Autonym : Deutsch (Deutschland)
EnglishName : German
LocalizedName : Deutsch (Deutschland)
ScriptName : Lateinisch
InputMethodTips : {0407:00000407}
Spellchecking : True
Handwriting : False
UPDATE: Ok seems like it works now (not that I changed anything?) - It changed everything for the local User profile, the thing i want is that it applied to the Welcome Screen and possible New User Profiles also is it possible to change the language for non unicode programs.
UPDATE 2: Okay after some testing It just downloads the new Pack but doesn't actually apply it - when the pack had already been downloaded it applies it - my question is - How do I apply the language pack without installing it manually?
Here you can see the Spanish language pack it says that it is available but my system language is still the same
Any idea how I can automate this process?
Thanks a lot!.