Add strings.

en.json

@@ -67,7 +67,10 @@
             "channel": {
                 "message_where": "Message {{channel_name}}",
                 "message_who": "Message {{person}}",
-                "message_saved": "Save to your messages"
+                "message_saved": "Save to your messages",
+                "uploading_file": "Uploading file...",
+                "failed_upload": "Failed to upload!",
+                "attached_file": "Attached {{filename}}"
             },
             "groups": {
                 "create": "Create a group.",