Idiocracy in full effect.
First of all, you are speaking *English. Don't you see the irony when you imbeciles talk out the side of your fat obese cheese burger eating mouths like that?
"Lit" is not an American slang it is just made popular by Muricans now. "Lit" means heavily drunk/crazy/extreme in a positive perception of the term and it was created in Britain... you know because the word is English... you know... the language you're writing in.

I am in my mid 20s now and have heard people say "it's lit" or "we're lit" since I could remember as a kid in the mid 90s so it's more prevalent throughout the world than you think. The first time I heard someone say something was "lit" in music was from Kurupt on Tha Chronic or Doggystyle that's damn near almost 30 years ago. So it's not a new slang term in fact just from a quick Google search the same slang term "lit" with the same meaning was created in Britain in 1910.
Receipts:
It's Lit
Be an American and think America invented everything, brehs. Typical.