Notice the spitter category of units.
Notice that they don't have jaws.
Now tell me, how does one talk without a jaw? Temporarily put your jaw out of action and try talking.
I hope you notice that it doesn't work.
But the spitter category still talk it off no problem. In fact, their speech isn't impaired at all.
But how does it work? Does World Zombination take place millions of years into the future, where humans have evolved to talk without jaws?
Perhaps the spitter is a phychic who can telepathically send his speech to those around him.
But probably the most obvious and despicable answer:
Proletariat made a mistake
Literally unplayable. I'm never touching a Proletariat game ever again.
(By the way don't mind all the text I just wrote. It's 2 am and I'm very tired)