Technically not true.
Throughout the movie, the T-1000 and the T-800 never directly speak to each other, because that’s a call back to the first movie where Kyle Reese and the T-800 never speak to each other directly.
However, the T-1000 and the T-800 do talk to each other for one scene, where they are impersonating another character!
The T-1000 killed Janelle and impersonated her while John is calling to see how his foster parents are doing. (Rather spooky scene too, because imagine if John never met the T-800 and went home by himself that night…)
The T-800 impersonated John Connor while it’s on the phone and calls the T-1000’s bluff by giving a fake name for the dog Max (“What’s wrong with Wolfie?”).
Why they never directly speak to each other? I guess they are busy with their mission—one to protect John and the other to kill John—so they do not waste time talking to each other and let their actions speak for themselves.