I apologize for the delay. We've been investigating this further and believe a simple code fix could fix this issue for you. We tested briefly, but don't have a fully functional multi-lingual site setup (just a dev site that tries to act like one). If you could try the following update and let us know if it works for you, that'd be wonderful.
The edit is in the /plugins/opengraph/k2/k2.php file. Around line 439, you should see:
$link = K2HelperRoute::getItemRoute($item->id . ":" . urlencode($item->alias), $item->catid);
Please update that to:
$link = K2HelperRoute::getItemRoute($item->id . ":" . urlencode($item->alias), $item->catid, $item->language);
Let us know how that goes. If it fixes things for you, we'll make sure to include it in the next release of JFBConnect.
Thanks!
Alex