Hi there,
i had the same problem as Naggenum. i put this code into my functions.php:
add_filter('gettext', 'translate_text_to_german', 20, 3);
function translate_text_to_german($ttxt, $txt, $d) {
   switch ($txt) {
     	case 'Submit':
         return 'Posten'; // Change text here
         break;
      
      	case 'Leave a Comment':
         return 'Kommentar hinterlassen'; // Change text here
         break;
      
	case 'Your Comment':
         return 'Ihr Kommentar'; // Change text here
         break;
   }
   return $ttxt;
}
It worked like a charm for the submit button. But the rest didnt change…
Take a look: http://2015.heidelberger-schloss-gastronomie.de/gruseldinner-jack-the-ripper/