HttpAcceptLanguage is a gem, which helps you detect the users preferred
language, as sent by the "Accept-Language" HTTP header.

The algorithm is based on RFC 2616, with one exception: when a user requests
"en-US" and "en" is an available language, "en" is deemed compatible with
"en-US". The RFC specifies that the requested language must either exactly match
the available language or must exactly match a prefix of the available
language. This means that when the user requests "en" and "en-US" is available,
"en-US" would be compatible, but not the other way around. This is usually not
what you're looking for.

WWW: https://github.com/iain/http_accept_language/