How to attach Gettext to Twig templates in YII2?

Question

Yii

Hello,
Can you tell me how to attach localization via Gettext to Twig templates in Yii2?
Installed via composer yiisoft/yii2-app-basic, added yiisoft/yii2-twig. Added to config:

'view' => [
        'renderers' => [
          'twig' => [
            'class' => 'yii\twig\ViewRenderer',
            'extensions' => [
              'Twig_Extensions_Extension_I18n'
            ],
          ],
        ],
      ],

The template engine works, you can render via $this->render('someaction.twig');
I also corrected the MessageSource in the config so that Yii::t uses PO files to store translations.

'i18n' => [
        'translations' => [
          'app*' => [
            'class' => 'yii\i18n\GettextMessageSource',
            'basePath' => '@app/messages',
            'sourceLanguage' => 'en-US',
          ],
        ],
      ],

Now how to tie Gettext specifically to Twig, so that you can use {{'some text'| trans}} in templates? I read the doc on Twig twig.sensiolabs.org/doc/extensions/i18n.html, but could not implement it.
In silex it was somehow like this:

$app->register(new Silex\Provider\TranslationServiceProvider(), array(
  'locale_fallbacks' => array('ru'),
));
$app['translator'] = $app->share($app->extend('translator', function($translator, $app) {
  $translator->addLoader('po', new PoFileLoader());
  $translator->addResource('po', __DIR__.'/../po/messages.en.po', 'en');
  return $translator;
}));
$app['twig']->addExtension(new Symfony\Bridge\Twig\Extension\TranslationExtension($app['translator']));
$app->before(function () use ($app) {
  $app['locale'] = 'ru';
});

//upd
Added "twig/extensions": "~1.1" dependencies and corrected the config for loading the Twig_Extensions_Extension_I18n extension. {{'translate me' | trans}} outputs a void now, but the function is known.
Another question is how to make it load translations from a given *.po file?

Answer 1

By analogy with Silex, it proxyed a translation request to the system \Yii::t, which can correctly load files with translations. The result is an extension

namespace app\components;

use Twig_Extension;
use Twig_Extensions_TokenParser_Trans;
use Twig_SimpleFilter;

class Twig_I18n_Extension extends Twig_Extension {

  /**
   * Translation message context
   * @var string
   */
  public $category = 'app';

  /**
   * Returns the token parser instances to add to the existing list.
   *
   * @return array An array of Twig_TokenParserInterface or Twig_TokenParserBrokerInterface instances
   */
  public function getTokenParsers()
  {
    return array(new Twig_Extensions_TokenParser_Trans());
  }

  /**
   * {@inheritdoc}
   */
  public function getFilters()
  {
    return array(
      new \Twig_SimpleFilter('trans', array($this, 'trans')),
    );
  }


  /**
   * @param string $category the message category.
   * @param string $message the message to be translated.
   * @param array $arguments
   * @param string $language the language code (e.g. `en-US`, `en`). If this is null, the current
   *  will be used.
   * @return string
   */
  public function trans($message, array $arguments = [], $category = null, $language = null)
  {
    if (!$category) {
      $category = $this->category;
    }
    return \Yii::t($category, $message, $arguments, $language);
  }

  /**
   * Returns the name of the extension.
   *
   * @return string The extension name
   */
  public function getName()
  {
    return 'i18n';
  }
}

The render settings are like this:

'view' => [
        'renderers' => [
          'twig' => [
            'class' => 'yii\twig\ViewRenderer',
            'extensions' => [
              'app\components\Twig_I18n_Extension'
            ],
          ],
        ],
      ],