yii2-bootstrap/docs/view_renderers.md

Yii2 view renderers

By default Yii uses PHP as template language but you can change it in your application. The component responsible for rendering a view using custom template enging is called viewRenderer. You can configure it as follows:

array(
	'components' => array(
		'viewRenderer' => array(
			'class' => 'yii\renderers\TwigViewRenderer',
			// or 'class' => 'yii\renderers\SmartyViewRenderer',
		),
	),
)

Twig

In order to use Twig you need to put you templates in files with extension .twig. Also you need to specify this extension explicitly when calling $this->render() or $this->renderPartial() from your controller.

Smarty

In order to use Smarty you need to put you templates in files with extension .tpl. Also you need to specify this extension explicitly when calling $this->render() or $this->renderPartial() from your controller.