Fix missing translation string in de-DE (#382)

* Fix missing translation string in de-DE

* Make placeholder for "paid by" field translatable

messages/en-US.json

@@ -160,6 +160,7 @@
       "categoryFieldDescription": "Select the expense category.",
       "paidByField": {
         "label": "Paid by",
+        "placeholder": "Select a participant",
         "description": "Select the participant who paid the expense."
       },
       "recurrenceRule": {
@@ -397,4 +398,4 @@
       "Water": "Water"
     }
   }
-}
+}