Twig_Environment::addExtension PHP Method

    public function addExtension(Twig_ExtensionInterface $extension)
    {
        $this->extensions[$extension->getName()] = $extension;
    }

 /**
  * @return \Twig_Environment
  */
 private function getTemplateEngine()
 {
     if (!$this->templateEngine instanceof \Twig_Environment) {
         $this->templateEngine = new \Twig_Environment($this->getFilesystemLoader(), ['cache' => realpath(PATH_CACHE), 'auto_reload' => true]);
         $this->templateEngine->addExtension(new \Twig_Extensions_Extension_I18n());
     }
     return $this->templateEngine;
 }