Hi @guidode, i have checked your site, seem liked you have a plugin which insert facebook api code or a theme that embedded facebook api code which language is english as default and that override mine. Please go to Appearance > Editor, and find below code :
<!-- ADD AN APPLICATION ID !! If you want to know how to find out your
app id, either search on google for: facebook appid, either go to https://rieglerova.net/how-to-get-a-facebook-app-id/
-->
<div id="fb-root"></div>
<script>
(function (d, s, id) {
var js, fjs = d.getElementsByTagName(s)[0];
if (d.getElementById(id)) return;
js = d.createElement(s);
js.id = id;
js.src = "//connect.facebook.net/en_US/all.js#xfbml=1&appId=540866125995567"; // addyour appId here
fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));
</script>
Do replace part of code “connect.facebook.net/en_US/all.js” become connect.facebook.net/de_DE//all.js
Or disable other facebook related plugin first to see how it goes.