When working on the Knights of the Old Republic Campaign Guide, Star Wars author Abel G. Peņa wrote a whole passage devoted to Nihilus' mask that was ultimately cut. It would have notably provided two scholarly explanations of Nihilus' speech. According to that cut passage, the Dark Lord's hissings may have been the first language ever spoken in the galaxy, or the raw dialect of the Force itself, untranslated by midi-chlorians.
So, Darth Nihilus was talking Forcesse by transmitting his intentions in the people's minds via Force visions?
__________________ RealistRacism: "Sheevites, much like the Banites, were meant to increase in power with each member. From Lightsnake to Gideon to Azronger, this was supposed to be the case. However, knowledge must've been lost in some kind of Gravid-like incident, as Az turned out to be a mid-tier debater with a sub-par track record, sh!itting all over Tempest's legacy. Sad."
Pretty sure it is first. Last makes no sense, though.
__________________ RealistRacism: "Sheevites, much like the Banites, were meant to increase in power with each member. From Lightsnake to Gideon to Azronger, this was supposed to be the case. However, knowledge must've been lost in some kind of Gravid-like incident, as Az turned out to be a mid-tier debater with a sub-par track record, sh!itting all over Tempest's legacy. Sad."
I think the hissings were actually his way to send/communicate his intentions through the Force and in individuals. And only those who suffered traumas would come to understand him.
__________________ RealistRacism: "Sheevites, much like the Banites, were meant to increase in power with each member. From Lightsnake to Gideon to Azronger, this was supposed to be the case. However, knowledge must've been lost in some kind of Gravid-like incident, as Az turned out to be a mid-tier debater with a sub-par track record, sh!itting all over Tempest's legacy. Sad."