Yii2 RESTful: Content Negotiation languages not work

I implemented a structure of API Rest with the models in Yii2. Everything works great for actions (index, create, update etc ...) and methods (GET, POST, PUT etc ..) but I have a problem with the ContentNegotiator class. Specifically, if I pass as a parameter of GET the language in which the response is to be translated, this is ignored. According to the documentation for setting the language of response we need to set allowed languages of ContentNegotiator (look at my behaviors()) and make a request like this:

http://localhost/api/v1/users?_lang=it-IT

But the response continues to be in English. Why??? Nothing against the English =)

This is my ActiveController child class that extend from yii\rest\Controller.

use yii\rest\ActiveController;
use yii\filters\VerbFilter;

class AActiveController extends ActiveController
{
    public function behaviors()
    {
        $behaviors = parent::behaviors();

        $behaviors['verbFilter'] = [
            'class' => VerbFilter::className(),
            'actions' => $this->verbs(),
        ];
        $behaviors['contentNegotiator']['languages'] = [
            'en-EN',
            'it-IT',
            'de-DE',
            'ru-RU',
        ];

        return $behaviors;
    }
...

N.B.: I debug through yii\filters\ContentNegotiator class of the framework and at this point the app language is set correctly but the response is always in English.

negotiate() public method

public function negotiate()
{
    $request = $this->request ?: Yii::$app->getRequest();
    $response = $this->response ?: Yii::$app->getResponse();
    if (!empty($this->formats)) {
        $this->negotiateContentType($request, $response);
    }
    if (!empty($this->languages)) {
        Yii::$app->language = $this->negotiateLanguage($request);
    }
    debug(Yii::$app->language); // result OK!: it-IT 
}

Looks like some build-in errors not translated, for example yii\rest\Action:103 throws throw new NotFoundHttpException("Object not found: $id") its not translated. You have different ways to solve this problem:

1. Good way. Extend this Action and throw correct exception with translate
2. Bad way. Edit framework file itself.
3. Best way. Create patch to framework and send to maintainers.

For more information about i18n see documentation.