it looks to me like it's not child language, but as though the barabrians had their own language and had to learn common, and being uncivilized made it more difficult to learn, so they speak poorly.
It seems like both races are connected to the land to some extent and casting chaos disrupts the balance within the land. It'd just seem wrong for them to cast necromancy. It's like a barbarian casting celestial, I think. I coulda sworn there was something in the rulebook about playing an insane...
From what I see, it's kind of a loophole thing. It seems that the hobling wouldn't break a promise, but he could find a way out of it. Such as "I promise to defend you with my life if you give me that sword!' hobling takes a death spell and recieves a life spell. "There, I'm done. I protected...