Alright sooo

What if... just the people that had lips/mouths/jaws could actually physically speak. (Sanford and Hank for example)

Zombies would also be able to speak, but as they're literally braindead they just make random noises lol.

Then people that don't have mouths (like Deimos or just everyday grunts) would speak either by sign language or writing in a sheet of paper, both which would be just common knowledge for literally anyone.

Of course not everyone would be equally as good at it. Normal grunts would only know basic stuff while people like Deimos or high skilled agents would know how to make more complex sentences.

And then there's also people that are extremely powerful and have telepathic abilities (like Tricky or the Auditor).

Those would speak telepathically while people would reply back with their toughts.

And also, I'm not counting the fact that everyone speaks on Madness: Project Nexus since I'm pretty sure it's an alternate timeline from the Madness series.