You absolutely can without much difficulty speak while being tased, if you have desensitized yourself to the pain, and/or if you have a particularly high pain tolerance (or ofcouse if you just lack the ability to feel pain in general).

Because the electrocution does not affect your ability to speak on a physical level, so it's all about having the will power and stocism to speak trough the pain.

Of course if it is your first time ever experiencing a shock of that magnitude it can easily disorient and stun (i know) you into remaining speechless.