In DanF's XML chart, there's the variable iWonderConstructRand, which has a min of 0 and a max of 50. There are 3 civ's with a value of 0: Bull, Monty, and Barbs. I think Anion assumed that 0 meant "never", since barbs are 0 and they never build wonders. OFC, this is not a valid assumtion, as many of us have observed Monty and Bull building wonders. It's probably just a weighting factor to increase/decrease the probability that a civ will build a given wonder, and there's probably also hard-coding somewhere to exclude barbs from building any at all.