I think the problem is trying to figure out the rules for such. In practice/theory its extremely simple "here say this". The question is whatever line of bullpoop I use trying to trick somebody into saying "this" does tricking somebody work? Or do they need to know what they are saying? If tricking works then my beguiler just loves the glibness spell, I could convince any body of damn near anything, for a time.
If "tricking" somebody into saying or attempting saying dark speech does not work, that means they must be aware, to a certain degree, what that they are doing is something wrong, bad and possible evil. Then the question is to what degree?
- victim needs to know what they are saying is a bad word, and possible evil; then I may still be able to convince "trick" them into saying dark speech, convincing them, this little transgression will aid them somehow.
- victim needs to know what they are saying is not only a bad word, but is most definitely evil and is used in pagan ritual, witchcraft & black magic. This would be a little harder for me to convince victim that saying the word is evil but will save little Jimmy, commit this little evil act for the greater good.
-OR
-victim needs to know what they are saying is a soul eating evil that will condemn them to an eternity of brimstone n anguish. Saying this word means you are attempting to unlock the mysteries of black magic.
Its suicide to try and say. Saying this word will never aid you in anything but evil, murder n death.... Ok so this one might require the glibness spell to pull off, if even that. Come to the Dark side its your only chance at saving padema. (spelling?)
My beguiler/mindbender is just trying to find as many no save scenarios as possible this is just one of them