<?php

$accepted_languages = array();

if(isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
    preg_match_all('#([a-z]{1,8}(-[a-z]{1,8})?)\s*(;\s*q\s*=\s*(1|0\.[0-9]+))?#i', $_SERVER['HTTP_ACCEPT_LANGUAGE'], $matches);
    if(count($matches[1]) > 0) {
        $accepted_languages = array_combine($matches[1], $matches[4]);
        foreach($accepted_languages as $language => $quality)
            if($quality === '')
                $accepted_languages[$language] = 1;
        arsort($accepted_languages, SORT_NUMERIC);
    }
}

echo '<pre>'.print_r($accepted_languages,1).'</pre>';