Chickens do understand some words. I use "no" when they are trying to come into my house or into the chick pen. The word alone without corresponding action doesn't do much. It does seem to help when I am also nudging them to go where I want them. However, I've never seen them respond to the word "no" all on its own.
On the other hand, they respond immediately to "come here, or come on" which tells me chickens are more responsive to positive action words. Chickens are easily trained using treat rewards as positive reinforcement. I clicker trained my young chicks in just a couple days, and they materialize as if by magic when I use the clicker.
People vastly underestimate the value of training chickens. It's really quite easy.