/Set-AllIntl: Sets the default system UI language, the language for non-Unicode programs, the "standards and formats" language ...

/Set-AllIntl:

  Sets the default system UI language, the language for non-Unicode programs,
  the "standards and formats" language and the input locales and keyboard
  layouts to the specified language in the mounted offline image.
  If used with any of the options used to specify the individual language or
  locales, then the individual settings take precedence.
  This command is not supported against an online image.

    Example:
      DISM.exe /Image:C:\test\offline /Set-AllIntl:en-US