lbry.com/controller/action/i18nActions.class.php

<?php

class i18nActions extends Actions
{
  public static function setCulture()
  {
    $culture = Request::getPostParam('culture');

    // Validate
    if ($culture && !in_array($culture, i18n::getAllCultures()))
    {
      $culture = null;
    }

    if ($culture)
    {
      Session::set(Session::KEY_USER_CULTURE, $culture);
    }
    else
    {
      Session::unsetKey(Session::KEY_USER_CULTURE);
    }

    //if session changes update domain
    //english language = www

    return Controller::redirect(Request::getHttpHeader('Referer', '/'));
  }
}