Required is the true language version of the OS, not the user interface language or the current locale settings.
Use case: software installation which has to apply security settings and user account creation. The scripts have to know certain system properties like user group names in the original language of the OS.
(Should work with Windows XP, Windows Server 2003, Vista, …)
To detect the operating system language use GetSystemDefaultUILanguage.
However, there are more straightforward ways to find things such as a known group name in Windows. For example, to get the name for the Users group call CreateWellKnownSid with
WellKnownSidType = 27 (WinBuiltinUsersSid)and then LookupAccountSid. The name for other well-known users and groups may be queried as well.