Nice way let user know email already exists via a flash message

As @ChicagoPhil said you can translate/change the messages and then you can use the helpers like form_error('email') to render the message where ever you like. if you really need to test if email has errors change your $email_exists statement like so

PHP Code:

if ($this->form_validation->error('email')) {
    $this->session->set_flashdata("email_exists", "The email address you provided already exists. Please signup.");
}