Talking can definitely be a problem. This is hugely frustrating not only does one have cancer, feels miserable from the treatment is uncertain about the outcome and now you cannot even communicate. This really does suck, especially when it seems that you are being sucked into conversations.
A pad may help to write own more complex things to complement the hand signals!!

Perhaps you may want to consider viscous lidocaine for short term relief for eating/drinking and talking. I also used this when I had meetings with my lab. You swish this around in your mouth and it provides instant relief. I diluted mine a bit to stretch it out some more.
Granted the relief is short but it allowed me to cut down on the over all amount of oxycodone/morphine I used (which comes with its own problem.... constipation, which also sucks as it is another thing you really do not want on top of all the other crap.

Markus