Language is an encoding scheme of our intelligence. It is enough to model our intelligence, I'm sure. But I don't think it is enough to build an intelligent agent. The agency that humans have I think is old and not rooted in our intelligence, rather it uses our intelligence. It's a carefully tuned array of interconnected processes in equilibrium that respond to disturbances in our environment, all encoded by our genetics. I suspect that part will be much harder to get right, as the nuance of building an agent like a biological social animal for example, is no doubt tremendous. Evolution has had a long time using trial and error to work out the issues. This is the part that unfortunately has the most potential to go terribly wrong.