<?php
    /*
      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 = $_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) &amp;&amp; ($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,$available_languages) &amp;&amp; (($qvalue*0.9) > $bestqval)) {
    $bestlang = $langprefix;
    $bestqval = $qvalue*0.9;
    }
    }
    return $bestlang;
    }
    ?>