Approval.

backend/iw/collection.json

@@ -53,6 +53,8 @@
         "up": "Up",
         "down": "Down",
         "main_image": "Main image",
-        "add_alternative_language": "All alternative language entry for this collection"
+        "add_alternative_language": "All alternative language entry for this collection",
+        "no_superordinate_collection": "No superordinate collection has been assigned",
+        "no_subordinate_collection": "No subordinate collection has been assigned"
     }
 }