Short answer : $this->dispatcher->getParam("YOUR_PARAM") 
I define it manually for more control over the URI as so:
/* file = routes.php */
$router->add("/english", [
  "namespace"  => "Api\Controllers",
  "module"     => "Api",
  'controller' => 'Language',
  'action'     => 'change',
  /* one of my params */ 'language'   => 'english'
]);
/* file = LanguageController.php */
<?php
namespace Api\Controllers;
use Phalcon\Mvc\Controller;
class LanguageController extends ControllerBase
{
  public function ChangeAction()
  {
   // get the param passed in the routes
    switch($this->dispatcher->getParam("language"))
    {
      case 'portuguese': $this->cookies->set("website_lang","pt"); break;
      case 'english':    $this->cookies->set("website_lang","en"); break;
    }
    $this->response->redirect("/");
  }
}