Nginx lang redirection depending on preferred user (accept) language

nginx-lang-conf

server {

    listen 80;
    charset UTF-8;

    # Language
    set $user_langs ",$http_accept_language";
    set $first_available_language "en";

    if ($user_langs ~* ',{1}(en|fr)') {
        set $first_available_language $1;
    }

    # Redirect root page depending on user and site languages
    rewrite ^/$ "$scheme://$host/$first_available_language" redirect;

    server_name mydomain.com www.mydomain.com ;
    …
}