A stab at user language localization by `User.user_lang`, a passed query param, or a stored session variable. This belongs in your AppController and should be called from the beforeFilter() method.

cake-user-language.php

<?php
/**
* Language Handler.
*
* Sets the app's configured language based on passed parameter or language
* configuration stored in session variable.
*
* @author C1V0
*/
protected function _langHandler() {
    if (!$this->Auth->User('user_lang')) { // If user language preference not set...
        if (isset($this->request->query['lang'])) { // Set session variable by query param
            $this->Session->write('Config.language', $this->request->query['lang']);
        }
    } else { // Use the user's language preference
        $this->Session->write('Config.language', $this->Auth->User('user_lang'));
    }
    // Set the language!
    if ($this->Session->check('Config.language')) { // Localize based on session variable
        Configure::write('Config.language', $this->Session->read('Config.language'));
    }
}