yii\i18n\MessageSource::init PHP Method

    public function init()
    {
        parent::init();
        if ($this->sourceLanguage === null) {
            $this->sourceLanguage = Yii::$app->sourceLanguage;
        }
    }

 /**
  * Initializes the DbMessageSource component.
  * This method will initialize the [[db]] property to make sure it refers to a valid DB connection.
  * Configured [[cache]] component would also be initialized.
  * @throws InvalidConfigException if [[db]] is invalid or [[cache]] is invalid.
  */
 public function init()
 {
     parent::init();
     $this->db = Instance::ensure($this->db, Connection::className());
     if ($this->enableCaching) {
         $this->cache = Instance::ensure($this->cache, Cache::className());
     }
 }