Language switch with sessions

[eluser]chris1986m[/eluser]
Hi at all,

this week i get a message, that the language switch problem is always there...
I become crazy...

So this morning i checked all my code again and split it.
Please, is there someone who can help?

Code:

$autoload['libraries'] = array('session', 'user_agent');
$autoload['helper'] = array('url', 'language');
$config['language'] = 'de';

start.php controller

Code:

class Start extends CI_Controller {
public function index() {
        $language = $this->session->userdata('language');
        $this->lang->load('main', $language);

  //Check language
  if ($language == '')
   $this->session->set_userdata('language', 'de');

        //Check mobile version
        if ($this->agent->mobile())
            $this->load->view('mobile');
        else
            $this->load->view('index');        
}
}

language.php controller

Code:

class Language extends CI_Controller {
public function set($language) {
  $this->session->set_userdata('language', $language);

  redirect('http://uuu.uu.uu/');
}
}

href="/language/set/en"
href="/language/set/de"

Please let me know if you have some ideas.
Thanks!