This is a setting for computers with more than one UI language installed. If you enable this setting the UI language of Windows ...

This is a setting for computers with more than one UI language installed. If you enable this setting the UI language of Windows menus and dialogs language for systems with more than one language is restricted to the specific language. If the specified language is not installed on the target computer or the policy is disabled, the language selection defaults to the language selected by the local administrator.