Unknown language ID in <SystemLocale> and <UserLocale> for language "English (World)"

[t-ekman]

Using the settings

Windows display language: English
Language: English (World)
Keyboard layout: Swedish
Home location: Sweden

It generates

<InputLocale>0409:0000041d</InputLocale>
<SystemLocale>en-001</SystemLocale>
<UILanguage>en-US</UILanguage>
<UserLocale>en-001</UserLocale>

According the MS "en-001" is not a valid Language ID
https://learn.microsoft.com/en-us/openspecs/office_standards/ms-oe376/6c085406-a698-4e12-9d4d-c3b0ee3dbc4a

[cschneegans]

I don't think that the Office Open XML File format specification is relevant here. en-001 is a valid language code and is supported by Windows, via both GUI and PowerShell:

PS> Set-WinUserLanguageList -LanguageList ( New-WinUserLanguageList -Language 'en-001' )

Confirm
Continue with this operation?
[Y] Yes  [N] No  [S] Suspend  [?] Help (default is "Y"): y
WARNING: If the Windows Display Language has changed, it will take effect after the next sign-in.
PS> Get-WinUserLanguageList


LanguageTag     : en-001
Autonym         : English (World)
EnglishName     : English
LocalizedName   : English (World)
ScriptName      : Latin
InputMethodTips : {2000:00000409}
Spellchecking   : True
Handwriting     : False

You are correct that <SystemLocale>en-001</SystemLocale> and/or <UserLocale>en-001</UserLocale> are seemingly not supported in autounattend.xml files. This needs further investigation, as there are other locales with numeric parts:

• ar-001
• en-001
• en-150
• eo-001
• es-419
• ia-001
• prg-001
• vo-001
• yi-001