Who did God appoint to be Moses' spokesman?

Answer: Aaron

God appointed Aaron the Levite to speak for Moses.

“Then the anger of the LORD burned against Moses, and He said, “Is not Aaron the Levite your brother? I know that he can speak well, and he is now on his way to meet you. When he sees you, he will be glad in his heart.”— Exodus 4:14 (BSB)