S.L.
Hi A.,
I have 2 daughters, one 8 and one 5. They both sometimes laugh in their sleep, and my oldest has been talking in her sleep for as long as I can remember! She has always had advanced language skills, and also has an active imagination. I never really questioned the sleep talking, it just seemed like an extension of her dreams. We have had mini conversations while she is sleeping, and if she seems anxious or scared I will always "direct" her thoughts to pleasant and comforting things. She never remembers doing it the next day, but will sometimes remember a related dream.
I don't really think you have anything to worry about, I hope I was able to help,