Add strings.

en.json

@@ -70,7 +70,12 @@
                 "message_saved": "Save to your messages",
                 "uploading_file": "Uploading file...",
                 "failed_upload": "Failed to upload!",
-                "attached_file": "Attached {{filename}}"
+                "attached_file": "Attached {{filename}}",
+                "typing": {
+                    "single": "{{user}} is typing…",
+                    "multiple": "{{userlist}} and {{user}} are typing…",
+                    "several": "Several people are typing…"
+                }
             },
             "groups": {
                 "create": "Create a group.",