Determine locale from browser settings

["Davide Ficano" <davide.ficano@xxxxxx>]

Actually the language used by portal is determinated by locale tag value 
inside xxx-config.xml file.

How can be overridden this value by browser setting?

Current scenario:

the xxx-config.xml file contains en (english language)
the browser is set to send fr http header (Accept-Language)
the portal is shown in english and user must **manually** switch to french.

Expected scenario:

the xxx-config.xml contains a "fallback" value used when the browser value 
doesn't match any configured locale on eXo.