Did you just translate all the cards for them?

Yeah, I just told them what the cards said. They could read the numerals for coins, so once they knew how the cards worked, that's all they needed.

Did you play with semi-open hands, so you could help translate any special ability cards they drew into their hand?

There are no hands in Machi Koro, all of the cards are played face up in a tableau. You're probably thinking of San Juan.