EN/DE code in Unattend.xml

Try following code in PowerShell:

$UnEncodedText = 'IamAdminPassword'

$EncodedText =[Convert]::ToBase64String([System.Text.Encoding]::Unicode.GetBytes($UnEncodedText))

write-host "Encoded_String_is:" $EncodedText

$EncodedText = 'SQBhAG0AQQBkAG0AaQBuAFAAYQBzAHMAdwBvAHIAZAA='

$DecodedText = [System.Text.Encoding]::Unicode.GetString([System.Convert]::FromBase64String($EncodedText))

write-host "Decoded_Text_is:" $DecodedText