Add rare hidden radio easter egg transmission

content/strings.en.json

@@ -21,6 +21,7 @@
   "radio.inaccurate": "Dispatch flags inaccuracies in your report (-%d).",
   "radio.received": "Dispatch received your report. Assistance en route.",
   "radio.emergency_dispatched": "Emergency responder dispatched.",
+  "radio.easter_egg": "¿Dónde está la mota?",
   "responder.arrived": "Responder arrives and %ss the situation.",
   "react.comply": "%s complies and steps back.",
   "react.leave": "%s turns and leaves.",