In episode 6th the old blind monk (Biwamaru) says that he did expect Hyakkimaru to go to fight the monster after he mentioned there was one, but not as soon as before he recovers from his wounds. But Hyakkimaru just recovered his hearing which he never had in his whole life, and with other sounds it seems he can't understand a thing he's hearing. Can Hyakkimaru understand what he hears or not?
Not initially, but in later episodes he seems to understand language. Like in Episode 12, Dororo tells Hyakkimaru that you have found your mother and you have a brother. He understands that. You can refer Episode 11 ("The Story of Banmon, Part 2") and Episode 12 "The Story of Banmon, Part 2" for the same. These episodes were released on March 18, 2019 and March 25, 2019 respectively.