After some googling, it doesn’t really seem like there is a lore/in universe explanation, which I find surprising after having the Disney EU and the legends EU. Some sith are named after a character quality, so maybe you could assume the dark side of the force revealed it to the master that named them?
How do the sith come up with these names anyways?
Are they always given by the master?
And what is the reason for doing this at all?
What does Darth Vader even mean?
After some googling, it doesn’t really seem like there is a lore/in universe explanation, which I find surprising after having the Disney EU and the legends EU. Some sith are named after a character quality, so maybe you could assume the dark side of the force revealed it to the master that named them?