diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 9bb36400..3527f3d2 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -20,17 +20,6 @@ Compatibility reports are always helpful. Use the "Compatibility Report" issue t
 
 Missing strings:
 
-* `es`
-    * `optionsMediaSyncElementDescription`
-    * `optionsReceiverSelectorCategoryName`
-    * `optionsReceiverSelectorCategoryDescription`
-    * `optionsReceiverSelectorType`
-    * `optionsReceiverSelectorTypeBrowser`
-    * `optionsReceiverSelectorTypeNative`
-    * `optionsReceiverSelectorWaitForConnection`
-    * `optionsReceiverSelectorWaitForConnectionDescription`
-    * `optionsReceiverSelectorCloseIfFocusLost`
-    * `optionsMirroringAppIdDescription`
 * `nl`
     * `popupMediaTypeApp`
     * `popupMediaTypeTab`
diff --git a/ext/src/_locales/es/messages.json b/ext/src/_locales/es/messages.json
index 89dcab75..4fd92aa0 100644
--- a/ext/src/_locales/es/messages.json
+++ b/ext/src/_locales/es/messages.json
@@ -193,6 +193,10 @@
         "message": "Sincronizar estado del receptor con el contenido"
       , "description": "Media casting sync checkbox label."
     }
+  , "optionsMediaSyncElementDescription": {
+        "message": "Sincroniza el estado (minuto de reproducción, volumen, subtítulos, etc...) entre el contenido y el dispositivo receptor."
+      , "description": "Media casting sync option description."
+    }
   , "optionsMediaStopOnUnload": {
         "message": "Detener reproducción del receptor al cerrar la página"
       , "description": "Media stop on unload checkbox label."
@@ -214,6 +218,38 @@
         "message": "Puerto del servidor HTTP:"
       , "description": "HTTP server port input label."
     }
+  , "optionsReceiverSelectorCategoryName": {
+        "message": "Selector de receptor"
+      , "description": "Options page receiver selector category title."
+    }
+  , "optionsReceiverSelectorCategoryDescription": {
+        "message": "Interfaz de selección del dispositivo receptor."
+      , "description": "Options page receiver selector category description."
+    }
+  , "optionsReceiverSelectorType": {
+        "message": "Tipo:"
+      , "description": "Receiver selector type option label."
+    }
+  , "optionsReceiverSelectorTypeBrowser": {
+        "message": "Navegador"
+      , "description": "Receiver selector type browser radio option label."
+    }
+  , "optionsReceiverSelectorTypeNative": {
+        "message": "Nativo"
+      , "description": "Receiver selector type native radio option label."
+    }
+  , "optionsReceiverSelectorWaitForConnection": {
+        "message": "Esperar conexión"
+      , "description": "Receiver selector wait for connection option checkbox label."
+    }
+  , "optionsReceiverSelectorWaitForConnectionDescription": {
+        "message": "Mantiene el selector de receptor abierto hasta que la sesión sea establecida o falle la conexión."
+      , "description": "Receiver selector wait for connection option description."
+    }
+  , "optionsReceiverSelectorCloseIfFocusLost": {
+        "message": "Cerrar al perder el foco"
+      , "description": "Receiver selector close if focus lost option checkbox label."
+    }
 
   , "optionsUserAgentWhitelistCategoryName": {
         "message": "Lista blanca de agentes de usuario"
@@ -282,6 +318,10 @@
         "message": "ID de aplicación receptora:"
       , "description": "Mirroring app ID input label."
     }
+  , "optionsMirroringAppIdDescription": {
+        "message": "ID de aplicación para una aplicación receptora de Chromecast registrada. Solo para uso avanzado. Debe ser compatible con la app predeterminada (véase el repositorio de GitHub)."
+      , "description": "Mirroring app ID option description."
+    }
 
   , "optionsReset": {
         "message": "Restaurar predeterminados"