In the Ósanwe-kenta, Tolkien describe how Valar, Maiar and the most powerful Children of Eru can communicate mentally and describe also how Melkor used that to torture its opponent's mind. However Tolkien also explain that the fences that protect one's spirit are really powerful and that Melkor decided that speech was a more powerful tool to use.
The Fall of Gondolin, even though it's an early work, also provides us with a detailed battle in which Balrogs are involved. Here they act more like some kind of totem or banner used to rally and galvanize Orcs around them, and you don't need to talk to do that, even though it's one of the ability of a commander in a Total War. In these games tactics are yours, the so-called "commanding" ability reflects more charisma in my opinion, and Balrogs sure don't lack charisma.