At first I thought this was a pregunta about how the writer came up with that name. That would be interesting to know. But apparently it is not. Lawliet is L's last name. tu learn this in "L Change the World".
I heard it's a British name... though I live in the UK and ain't ever heard the name before. Maybe it's old-fashioned? I'll be hyped when I find someone with the name though. Prove it's his name; It's in "L Changes the World" movie. Don't know about the novel as I yet to read it. It's also in Death Note 13: How to Read. It's in his bio saying it's his true name. The book also comes with a True Name card. (Which looks awesome, btw.) Which also has the name "L Lawliet" on it. I believe it's pronounced Law-Leet. Though I could be wrong. But that's how I say it as that makes the most sense to me.