engelsystem/includes/funktion_flag.php

<?php
   if(strpos($_SERVER["REQUEST_URI"], "?") > 0)
    $URL = $_SERVER["REQUEST_URI"] . "&SetLanguage=";
  else
    $URL = $_SERVER["REQUEST_URI"] . "?SetLanguage=";

  echo "<a href=\"" . $URL . "DE\"><img src=\"" . $url . $ENGEL_ROOT . "pic/flag/de.gif\" alt=\"DE\" /></a> ";
  echo "<a href=\"" . $URL . "EN\"><img src=\"" . $url . $ENGEL_ROOT . "pic/flag/en.gif\" alt=\"EN\" /></a> ";
?>