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<?php
    /*
     * Source: http://www.php.net/manual/en/function.http-negotiate-language.php
     * By Anonymous
     */

    /**
     * determine which language out of an available set the user prefers most
     *
     * $available_languages        array with language-tag-strings (must be lowercase) that are available
     * $http_accept_language    a HTTP_ACCEPT_LANGUAGE string (read from $_SERVER['HTTP_ACCEPT_LANGUAGE'] if left out)
     */
    function prefered_language($available_languages,
          $http_accept_language = "auto")
    {
      // if $http_accept_language was left out, read it from the HTTP-Header
      if ($http_accept_language == "auto")
        $http_accept_language = isset($_SERVER['HTTP_ACCEPT_LANGUAGE']) ? $_SERVER['HTTP_ACCEPT_LANGUAGE']
                : '';

      // standard  for HTTP_ACCEPT_LANGUAGE is defined under
      // http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4
      // pattern to find is therefore something like this:
      //    1#( language-range [ ";" "q" "=" qvalue ] )
      // where:
      //    language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
      //    qvalue         = ( "0" [ "." 0*3DIGIT ] )
      //            | ( "1" [ "." 0*3("0") ] )
      preg_match_all("/([[:alpha:]]{1,8})(-([[:alpha:]|-]{1,8}))?" .
            "(\s*;\s*q\s*=\s*(1\.0{0,3}|0\.\d{0,3}))?\s*(,|$)/i", $http_accept_language, $hits, PREG_SET_ORDER);

      // default language (in case of no hits) is the first in the array
      $bestlang = $available_languages[0];
      $bestqval = 0;

      foreach ($hits as $arr) {
        // read data from the array of this hit
        $langprefix = strtolower($arr[1]);
        if (!empty($arr[3])) {
          $langrange = strtolower($arr[3]);
          $language = $langprefix . "-" . $langrange;
        } else
          $language = $langprefix;
        $qvalue = 1.0;
        if (!empty($arr[5]))
          $qvalue = floatval($arr[5]);

        // find q-maximal language
        if (in_array($language, $available_languages) && ($qvalue > $bestqval)) {
          $bestlang = $language;
          $bestqval = $qvalue;
        }
        // if no direct hit, try the prefix only but decrease q-value by 10% (as http_negotiate_language does)
        else if (in_array($langprefix, $available_languages) && (($qvalue * 0.9) >
              $bestqval)) {
          $bestlang = $langprefix;
          $bestqval = $qvalue * 0.9;
        }
      }
      return $bestlang;
    }