i18n: update locale es.js (#17419)

src/locale/lang/es.js

@@ -106,10 +106,10 @@ export default {
       hasCheckedFormat: '{checked}/{total} revisados'
     },
     image: {
-      error: 'FAILED' // to be translated
+      error: 'HA FALLADO'
     },
     pageHeader: {
-      title: 'Back' // to be translated
+      title: 'Volver'
     }
   }
 };