root/trunk/apps/main/lib/i18nSubdomainFilter.class.php

<?php
class i18nSubdomainFilter extends sfFilter
{

  /**
   * Log filter activity
   *
   * @param string  $message
   * @param int     $level
   */
  public function log($message, $level = sfLogger::DEBUG)
  {
    sfContext::getInstance()->getLogger()->log('{i18nSubdomainFilter} '.$message, $level);
  }

  /**
   * Executes filter chain
   *
   * @param sfFilterChain $filterChain
   */
  public function execute($filterChain)
  {
    if ($this->isFirstCall())
    {
      $context = $this->getContext();
      $request = $context->getRequest();
      $user    = $context->getUser();
      $host_parts = explode('.', $request->getHost());

      if (count($host_parts) > 2) // We have at least a subdomain
      {
        $lang = strtolower($host_parts[0]);
      }
      else
      {
        $lang = sfConfig::get('sf_default_culture', 'en');
      }

      $this->log(sprintf('Desired lang extracted from host: %s', $lang));

      $enabled_cultures = sfConfig::get('app_cultures_enabled', array());
      if (in_array($lang, $enabled_cultures))
      {
        $this->log(sprintf('Applying detected requested lang to session: %s', $lang));
        $user->setCulture($lang);
        sfConfig::set('sf_current_culture', $lang);
        $context->getResponse()->addMeta('language', $lang, true);
      }
    }
    $filterChain->execute();
  }

}