get-client-language.php

<?php

define('WP_USE_THEMES', false);

require( dirname(__FILE__) . '/wp-load.php' );

/**
 * Return WPML defined language codes
 * @return Array
 */
function getAvailableLanguages(){
    $langs = icl_get_languages();
    $langs = array_keys($langs);
    return $langs;
}

/**
 * Return available client language choosen from $availableLanguages array
 */
function getClientLanguage($availableLanguages = null, $default='en'){
    if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
        $langs=explode(',',$_SERVER['HTTP_ACCEPT_LANGUAGE']);
        //start going through each one
        foreach ($langs as $value){
            $choice=substr($value,0,2);
            if(in_array($choice, $availableLanguages)){
                return $choice;
            }
        }
    }
    return $default;
}

header("Location: ". site_url() ."/". getClientLanguage( getAvailableLanguages() ), true, 302);