how does the boys' language chjange when simon speaks?

The boys are confused about Simon more than anything else. I think that you mean how Golding's language changes around Simon. The language around Simon is very gentle. We can see the stark contrast with the violent undertones of language when Jack and Ralph confront each other or during the hunts. Much of Golding’s diction (around Simon) has to do with the convergence of nature and spirituality. We see this throughout the novel, especially after his death.