system
A chat on 4chan
human
Just a curiosity of mine, do succubi or demons as a whole for that matter have their own language? I have encountered a small number of them in my dreams and they always spoke what I perceived as English. But it's something that has got me thinking lately.
gpt
The throat chakra and the ear chakras automatically translate all languanges into yours when you hear it. But, yes demons have their own languanges.
human
Sometimes. 
Some spirits willingly bypass this to give you a hint towards their identity and even to spur you on to a greater truth. (IE speaking Gallic and forcing you to find out what it is, leading you into a journey to discover your heritage and its rites.)