yii2fullcalendar\CoreAsset::registerAssetFiles PHP Method

    public function registerAssetFiles($view)
    {
        $language = $this->language ? $this->language : Yii::$app->language;
        if (strtoupper($language) != 'EN-US') {
            $this->js[] = "locale/{$language}.js";
        }
        if ($this->googleCalendar) {
            $this->js[] = 'gcal.js';
        }
        parent::registerAssetFiles($view);
    }