To translate the fields and texts of default contact form
Go to the inc/custom-functions.php file
at line no. 780 find contact form code and translate the fields into German language
You can also send your website URL and WordPress admin login details at firstname.lastname@example.org so we can check and solve your problem regarding default contact form or contact form 7 WordPress plugin.
But if i translate the fields as suggested, my changes will be lost at the next update of the theme. Is it possible for you to make the fields and text configurable like you did with other fields in Theme Options?