This setting restricts users to the specified language by disabling the menus and dialog box controls in the Regional and ...

This setting restricts users to the specified language by disabling the menus and dialog box controls in the Regional and Language Options Control Panel. If the specified language is not installed on the target computer, the language selection defaults to English.

To enable this policy in Windows Vista, you need to use "Restricts the UI languages Windows should use for the selected user" policy.