"Are you ready then? On you go!"
Translation:A bheil thu deiseil ma-thà? Stiall ort!
Hmmm, I wonder if the derivation is from giving a slap of the reins (a stripe) to a horse, to get the horse to move on. Just a guess. I was wondering about the "on you go" translation too. Here in the States, we don't tend to say that-- we would say, "let's go" or "there you go."