His younger brother has mutism and cannot speak.

He was completely silent and said nothing.

He kept silent without saying anything.

He talked about his trip.

I like talking with him.

He kept talking to me for a long time.

He continued to maintain silence.

He continued to maintain silence.

His younger brother has mutism and doesn't speak a word in front of people.

Because he suffers from selective mutism, it's difficult for him to speak.