Approval.

backend/es/sources.json

@@ -65,6 +65,8 @@
         "license_explica": "The license of the source or the digitized version thereof.",
         "source_fulltext": "Full text",
         "editor": "Editor",
-        "editor_explica": "Editor or editors of this work. Type in and select an editor from the list. If none can be found, you can add a new one by clicking on the \"+\"-button in front of the text field."
+        "editor_explica": "Editor or editors of this work. Type in and select an editor from the list. If none can be found, you can add a new one by clicking on the \"+\"-button in front of the text field.",
+        "booktitle": "Book title",
+        "booktitle_explica": "The book a chapter was published in."
     }
 }