function change_language() {
	var lang = document.getElementById('lang');
	var curr_url = location.href;
	var aanwPar = curr_url.indexOf('?');
	if(aanwPar == -1) {
		var url = location.href + "?lang=" + lang.value;
	} else {
		var url = location.href + "&lang=" + lang.value;
	}
	
	window.location=url;
}