Unvanquished is an open-source FPS game featuring team-based strategy and RTS elements, pitting humans against aliens in a futuristic setting.
https://forums.unvanquished.net/
Bots are fine (especially compared to urban terror bots), Fuma did a great job. Would be nice if the bots could talk, insult, taunt, provoke. as in quake 3.
in quake3 you can modify the dialogues of of the bots (its a text file) so you can even translate the dialogues into another language, or make them talk harder :)
They should definitely use vsays to tell you what they are about to do. That would even help debugging them, given that currently the only way to do so is gdb. 
The existing behavior tree system does have limited "say" and "teamsay" actions available which take a string argument.
The best course of action would be to break up the current high level actions into their own behavior tree based behaviors ( e.g. action fight becomes a bunch of sequences, selectors, and conditions and low level actions like "fire" ). Then you could add say actions wherever you want among the behavior's code. Long ago, I nearly broke up the fight action ( which is definitely the most complex of all the behaviors ) just using behavior tree logic, so it is definitely possible.
The current system allows you to integrate these complex behaviors just by using "behavior <filename>" where <filename> is the name of a file that contains the other behavior tree.
I'm rather busy with real life atm, so I don't think I will be able to do this myself.