In my DJ, I remember exact quotes enough, but a lot of the time there is just the “I said…they said…she said…” without really hearing them. So is it possible that most of the time in dreams people talk through their heads?
Of course, in really vivid dreams I remember more quotes, so it could jsut be poor recall in that sense.
Hmm. I don’t remember ever talking, in the traditional sense, in any of my NDs. And strangely enough, in my LDs, I’m too busy doing other cool stuff to talk to people. (haven’t had the chance to talk with DCs) Although… in LD #2, I talked to myself verbally. 
As it is with me - most talking are soundless. But there are exceptions, because you can hear in dreams.
I have real speech in my dreams. But I don’t have extended dialogue.
me neither (my recurring DC is also quite quiet) i speak mostly “soundless”
In both Lucid and Normal dreams for myself I find that I on the occassion can “hear” the voice of another/myself. Although, I never seem to speak outloud to myself - which I do quite often IRL due to habbit.
As for communicating by thought - I believe that would be the most common way of communication in dreams - but if you are more awake you can start to use your “hearing” sense more and then the communication can be done by “speaking”+“hearing it”.