The pinging sound is chat. In the lower right of your screen you should seen a black circle with 2 message bubble images. That’s chat. Click on that to open it and there will be a gear symbol. You can choose from there to go offline or mute the chat notifications.

I think you will only know that someone saw your request if the person either responds to you or accepts the request. By the way the “request language exchange” button is really more of a “friend request”. It doesn’t start a chat or anything – it just adds the person to your friend list (if it is accepted).