Inside Messages > Requests > Users.cs add under the ChangeLook() void this:

        private void ChangeMotto()
        {
            string RequestMotto = Request.PopFixedString();

            string Motto = UberEnvironment.FilterInjectionChars(RequestMotto.Substring(35));

            if (Motto == Session.GetHabbo().Motto) // Prevents spam?
            {
                return;
            }

            Session.GetHabbo().Motto = Motto;

            using (DatabaseClient dbClient = UberEnvironment.GetDatabase().GetClient())
            {
                dbClient.AddParamWithValue("motto", Motto);
                dbClient.ExecuteQuery("UPDATE users SET motto = @motto WHERE id = '" + Session.GetHabbo().Id + "' LIMIT 1");
            }

            if (Session.GetHabbo().InRoom)
            {
                Room Room = Session.GetHabbo().CurrentRoom;

                if (Room == null)
                {
                    return;
                }

                RoomUser User = Room.GetRoomUserByHabbo(Session.GetHabbo().Id);

                if (User == null)
                {
                    return;
                }

                ServerMessage RoomUpdate = new ServerMessage(266);
                RoomUpdate.AppendInt32(User.VirtualId);
                RoomUpdate.AppendStringWithBreak(Session.GetHabbo().Look);
                RoomUpdate.AppendStringWithBreak(Session.GetHabbo().Gender.ToLower());
                RoomUpdate.AppendStringWithBreak(Session.GetHabbo().Motto);
                RoomUpdate.AppendInt32(Session.GetHabbo().GetAchievementScore());
                Room.SendMessage(RoomUpdate);
            }

            UberEnvironment.GetGame().GetAchievementManager().UnlockAchievement(Session, 5, 1);
        }

Inside Messages > Requests > Users.cs add under "RequestHandlers[44] = new RequestHandler(ChangeLook);" this:

RequestHandlers[484] = new RequestHandler(ChangeMotto);

THANKS FOR ADDING, FINALLYYY!!! :D, I'm not sure if that substring thingie works fine, but should do the job..