yii2-bootstrap/docs/view_renderers.md

Yii2 view renderers

By default Yii uses PHP as template language but you can configure it to be able to render templates with special engines such as Twig or Smarty.

The component responsible for rendering a view is called view. You can add a custom template engines as follows:

array(
	'components' => array(
		'view' => array(
			'class' => 'yii\base\View',
			'renderers' => array(
				'tpl' => array(
					'class' => 'yii\renderers\SmartyViewRenderer',
				),
				'twig' => array(
					'class' => 'yii\renderers\TwigViewRenderer',
				),
				// ...
			),
		),
	),
)

Twig

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

echo $this->render('renderer.twig', array('username' => 'Alex'));

Smarty

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

echo $this->render('renderer.tpl', array('username' => 'Alex'));