fix typo and missing messages (#5902)

i18n/en.json

@@ -416,7 +416,7 @@
     "translation": "Tried to perform an invalid update of the default channel {{.Channel}}"
   },
   {
-    "id": "api.channel.update_last_viewed_at.get_unread_count_for_channel.errord",
+    "id": "api.channel.update_last_viewed_at.get_unread_count_for_channel.error",
     "translation": "Unable to get the unread count for user_id=%v and channel_id=%v, err=%v"
   },
   {