Simple PyroCMS module (event) that sets the language based on first uri segment, so that content stored under e.g. /da will make PyroCMS (CI) run as "danish". Create a folder in any "module" directory named i18n and add these files, and install module using the admin panel

details.php

<?php

defined('BASEPATH') or exit('No direct script access allowed');

/**
 * i18n details file
 * 
 * @author      Kim Henriksen <kh@ipimp.at>
 * @package 	PyroCMS
 * @subpackage  i18n Module
 * @category	module class
 */
class Module_i18n extends Module
{

    public $version = '1.0.0';

    public function info()
    {
        return array(
            'author' => 'Kim Henriksen',
            'name' => array(
                'en' => 'i18n'
            ),
            'description' => array(
                'en' => 'Kim Henriksen i18n Module.'
            ),
            'frontend' => FALSE,
            'backend' => FALSE,
        );
    }

    public function install()
    {
        return TRUE;
    }

    public function uninstall()
    {
        return TRUE;
    }

    public function upgrade($old_version)
    {
        // Your Upgrade Logic
        return TRUE;
    }

    public function help()
    {
        // Return a string containing help info
        // You could include a file and return it here.
        return "Some Help Stuff";
    }

}

/* End of file details.php */

events.php

<?php

defined('BASEPATH') OR exit('No direct script access allowed');

/**
 * i18n Events Class
 * 
 * @package     PyroCMS
 * @subpackage  i18n Module
 * @category    events
 * @author      Kim Henriksen <kh@ipimp.at>
 */
class Events_i18n
{

	/**
	 * CodeIgniter
	 * @var type 
	 */
	protected $CI;

	/**
	 * Language config
	 * @var array
	 */
	protected $config;

	/**
	 * Event constructor
	 * registers this event
	 */
	public function __construct()
	{
		// We don't wan't to mess around with /admin panel
		if (preg_match('@\/admin(\/.+)?$@', $_SERVER['REQUEST_URI']))
		{
			return;
		}

		$this->CI = & get_instance();
		
		// Load helper
		$this->CI->load->helper('i18n/i18n');

		// register the public_controller event when this file is autoloaded
		Events::register('public_controller', array($this, 'run'));

		require APPPATH . '/config/language.php';
		$this->config = $config;
	}

	/**
	 * Event run
	 */
	public function run()
	{
		// Get language code segment
		$code = $this->_get_language_code_segment();
		
		// If the current CI language (CURRENT_LANGUAGE) is not equal 
		// to the the first URI segment we are under 
		// override session language code and refresh the page.
		if ($this->_is_valid_language_code($code) AND CURRENT_LANGUAGE !== $code)
		{		
			change_language($code);
		}
		
	}

	/**
	 * Check if the code is a valid language code, and is supported
	 * @param string $code
	 * @return boolean
	 */
	protected function _is_valid_language_code($code)
	{
		if (strlen($code) === 2 AND array_key_exists($code, $this->config['supported_languages']))
		{
			return TRUE;
		}

		return FALSE;
	}

	/**
	 * Returns language code based on first uri segment
	 * if no valid language could be found in first segment (or it doesn't exist)
	 * the default language code is returned 
	 * @return string
	 */
	protected function _get_language_code_segment()
	{
		// Get the first uri segment
		// If it's exactly to chars long, we treat it as a language segment
		// (if the first uri segment doesn't exist, the default language is used
		if (strlen($code = $this->CI->uri->segment(1, $this->config['default_language'])) === 2)
		{
			return $code;
		}
		// If the first segment is not of 2 chars lenght, we imagine that 
		// the first segment is the default language string
		else
		{
			return $this->config['default_language'];
		}
	}

}

/* End of file events.php */

i18n_helper.php

<?php

if (!function_exists('change_language'))
{

	/**
	 * Overwrites the session lang code and reloads the (current) url
	 * also preserves query strings if any
	 * @param string $code
	 * @param string $url optional url instead of current url
	 */
	function change_language($code, $url = NULL)
	{
		$CI = & get_instance();

		// Overwrite the language session code
		// which is created by the pick_language hook 			
		$_SESSION['lang_code'] = $code;

		if (empty($url))
		{
			$base = $CI->config->site_url($CI->uri->uri_string());
			$url = $_SERVER['QUERY_STRING'] ? $base . '?' . $_SERVER['QUERY_STRING'] : $base;
		}

		// Refresh the page
		redirect($url, 'location');
	}

}

We have an english frontpage, we just slugged it "en/"

and then we added every english page as a child of that page