That doesn't explain why the orders in the game are materialized as if the commander is speaking to you. You are correct about horns, musical instruments, and signal flags being used for orders, but they were far from the only methods, even in the most organized pre-modern armies such as the Romans, you need to have direct human communication in order to coordinate something so complicated. In smaller skirmishes, shouting orders was probably sufficient in many situations, but commanders speaking to each other, sending runners or riders in larger battles, is obviously necessary. You can't really replicate that in this game though. I'd rather have the orders that appear on-screen show up as just the rudimentary directions without your name, as if it's translating the horn blows, rather than it being as if the commander is sending text messages to you in those text dialogues. It's not a huge deal to me as is the system just working as it should be, but it is immersion-breaking.