Simple stuff like "Lets go team!", "Well done everyone!", "We can do this!".

Include cringy/funny stuff like "I am a potty mouth and I have hopefully learned my lesson". "I will be nice to my teammates from now on".

Make it obvious that its AI made because 1) The restricted player cant do anything about it. 2) It would lift team moral up because its funny. 3) It would actually make it obvious that you have a restricted player on your team and you cant really communicate complicated map plays with them.

It just adds positive vibes to chat with 0 downside.