http_negotiate_language: get langauge form Accept Language header

negotiate_language.php

<?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 $_SERVER['HTTP_ACCEPT_LANGUAGE'] if left out) 
*/ 
function negotiate_language ($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; 
} 
?>