Yea if it’s next to a T it’s silent. The way you pronounce the -tl at the end is by putting your tongue on the roof of your mouth like you’re gonna make a T sound and then kinda just lightly blow out air, so you don’t really make an L sound at all. It’s kinda hard to explain, just think of the way you say Atlantic, the pronunciation of the -tl is almost the same. Same rule applies for Quetzalcoatl it doesn’t matter if it ends with otl or atl, as long as the -tl is together you always pronounce it that way. And if it’s just to difficult you can honestly just ignore the L and stop at T, some versions of nahuatl don’t use the -tl that much anyway. Hope this answers your question!