The GetLocale method returns a number that identifies the locale for the specified message set.
MessageManager.GetLocale(MessageSet)
If this parameter is not specified, GetLocale returns the locale for the message set to which you have initialized the MessageManager’s DefaultLanguage property.
Like GetMessage, GetLocale is usually not called from within a site. Instead, it is used by the OPP to retrieve the locale for a message that describes an error that the OPP has encountered during a purchase.