Fixed #4.

functions.php

@@ -65,6 +65,7 @@ function create_post_types() {
       'has_archive' => true,
       'menu_icon' => 'dashicons-calendar-alt',
       'supports' => array('title', 'editor', 'thumbnail'),
+      'rewrite' => array('slug' => 'tag-der-architektur'),
     )
   );