MY_Controller.php

<?php

    /* Defining the language */
    private function _define_language()
    {
        $uri = $this->uri->segment(1);
        if ( 'admin' != $uri )
        {
            if ( !empty($uri) )
            {
                $current_language = $this->uri->segment(1);
                ('pt' == $uri ? $this->lang->load($this->router->class, 'portuguese') : $this->lang->load($this->router->class, 'english'));
                $this->lang->load('application', 'english');
            }
            else
            {
                $current_language = 'pt';
                $this->lang->load($this->router->class, 'portuguese');
                $this->lang->load('application', 'portuguese');
            }
            $this->data['current_lang'] = $current_language;
        }
    }

MY_lang.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');

// CodeIgniter i18n library by Jérôme Jaglale
// http://maestric.com/en/doc/php/codeigniter_i18n
// version 10 - May 10, 2012

class MY_Lang extends CI_Lang {

    /**************************************************
     configuration
    ***************************************************/

    // languages
    var $languages = array(
        'en' => 'english',
        'pt' => 'portuguese'
    );

    // special URIs (not localized)
    var $special = array(
        "admin", "login", "logout"
    );

    // where to redirect if no language in URI
    var $default_uri = '';

    /**************************************************/


    function __construct()
    {
        parent::__construct();
        global $CFG;
        global $URI;
        global $RTR;

        $segment = $URI->segment(1);

        if (isset($this->languages[$segment]))  // URI with language -> ok
        {
            $language = $this->languages[$segment];
            $CFG->set_item('language', $language);

        }
        else if($this->is_special($segment)) // special URI -> no redirect
        {
            return;
        }
        else    // URI without language -> redirect to default_uri
        {
            // set default language
            //$CFG->set_item('language', $this->languages[$this->default_lang()]);

            // redirect
            //header("Location: http://" . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'].$this->default_uri);
            //exit;
        }
    }

    // get current language
    // ex: return 'en' if language in CI config is 'english'
    function lang()
    {
        global $CFG;
        $language = $CFG->item('language');

        $lang = array_search($language, $this->languages);
        if ($lang)
        {
            return $lang;
        }

        return NULL;    // this should not happen
    }

    function is_special($uri)
    {
        $exploded = explode('/', $uri);
        if (in_array($exploded[0], $this->special))
        {
            return TRUE;
        }
        if(isset($this->languages[$uri]))
        {
            return TRUE;
        }
        return FALSE;
    }

    function switch_uri($lang = null)
    {
        $CI =& get_instance();
        $uri = $CI->uri->uri_string();
        if ($uri != "")
        {
            $exploded = explode('/', $uri);
            if($exploded[0] == $this->lang())
            {
                $exploded[0] = $lang;
            }
            $uri = implode('/',$exploded);
        }
        return $uri;
    }

    // is there a language segment in this $uri?
    function has_language($uri)
    {
        $first_segment = NULL;

        $exploded = explode('/', $uri);
        if(isset($exploded[0]))
        {
            if($exploded[0] != '')
            {
                $first_segment = $exploded[0];
            }
            else if(isset($exploded[1]) && $exploded[1] != '')
            {
                $first_segment = $exploded[1];
            }
        }

        if($first_segment != NULL)
        {
            return isset($this->languages[$first_segment]);
        }

        return FALSE;
    }

    // default language: first element of $this->languages
    function default_lang()
    {
        foreach ($this->languages as $lang => $language)
        {
            return $lang;
        }
    }

    // add language segment to $uri (if appropriate)
    function localized($uri)
    {
        if($this->has_language($uri)
                || $this->is_special($uri)
                || preg_match('/(.+)\.[a-zA-Z0-9]{2,4}$/', $uri))
        {
            // we don't need a language segment because:
            // - there's already one or
            // - it's a special uri (set in $special) or
            // - that's a link to a file
        }
        else
        {
            $uri = $this->lang() . '/' . $uri;
        }

        return $uri;
    }

}

/* End of file */