Block Wiki index.php queries without language header
    
    Recently lots of malicious traffic hitting index.php on the various
    language wikis is observed, originating from quickly changing
    IP networks and utilizing random user agents.
    Upon analysis of a pattern to block, modern web browsers were found to
    always incorporate a "Accept-Language" header, whilst bots/scripts do not.
    A filter is implemented on the relevant requests, returning 406 if no
    "Accept-Language" header is present.
    This does inhibit tools such as curl and wget as well, however use of
    such towards index.php is not common, and if needed, the header can easily
    be added by legitimate users.
    
    Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>