kartik\social\FacebookPlugin::registerAssets PHP Method

    protected function registerAssets()
    {
        $view = $this->getView();
        $async = $this->async ? "js.async = true;" : "";
        $lang = str_replace('-', '_', $this->language);
        $js = <<<SCRIPT
(function(d, s, id) {
    var js, fjs = d.getElementsByTagName(s)[0];
    if (d.getElementById(id))
        return;
    js = d.createElement(s);
    js.id = id;
    {$async}
    js.src = "//connect.facebook.net/{$lang}/sdk.js#xfbml=1&appId={$this->appId}&version=v2.0";
    fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));                
SCRIPT;
        $view->registerJs($js);
    }