Method to determine if a user has overridden the browser's default locale. For example, this method can be used to
check for the existence of a cookie which defines a user's preferred locale. Returning null will cause
PingFederate to fall back to its default locale handling.
request - The HttpServletRequest can be used to read cookies, parameters, headers, etc. Accessing the HttpSession from
the request is not recommended and doing so is deprecated. Use
SessionStateSupport as an alternative.
The user's preferred locale. Return null if the user has not overridden the default locale.