The locale code can be either a 2 letter language code defined by ISO 639-1, for example 'en', or a [language]-[country] code as allowed by the HTTP Accept-Language header, for example 'en-us' or 'en-gb'. Please refer to http://www.loc.gov/standards/iso639-2/php/English_list.php and http://www.w3.org/International/questions/qa-accept-lang-locales
The locale will only be available if SetLocale has been called on the user information object or if the user information was initialized with a session identifier.