Lookup an old AI text program called 'ELIZA'. It keeps keywords in a small database and reformats its replies based on the keyword detection. Update the keywords and the 'I don't understand' response.
It comes back with reasonable replies about 60 to 70% of the time and you can cover the other 40% or so with the "I'm busy" or "What? Didn't catch that, I'm in combat."
Make sure you do the following:
A) Make it pause about 1 to 5 seconds before responding.
B) Make random typo's appear every so often (transpose two letters, double a letter, or drop a random letter off).
C) Have the first GM /whisper be something like 'Checking for bots, eh?

' or 'No bots here, move along.'
Just a thought. Eliza was pretty good at responding back considering it was written in about 100 lines of code.