app_2.php

<?php

$app->get('/lang/{lang}', function($lang) use($app) {
	/*
	 * check if language exists
	 */
	if (is_dir(__DIR__ . '/locale/' . $lang)) {
		/* save user selection in session */		
		$app['session']->set('current_language', $lang);		
	}
	
	return $app->redirect($_SERVER['HTTP_REFERER']);
});