And I found this lengthy monologue from the book Les Miserables, which I'll copy down here, first in the French argot, then in the translated English (as thieves' cant), and then the plain English.
Note that where and how slang is used isn't exactly equivalent between the two languages. Don't feel obligated to copy exactly how it is used here, but feel free to improvise a bit, how would your conlang speakers communicate the same material?
French argot
Qu’est-ce que tu nous bonis là ? Le tapissier n’aura pas pu tirer sa crampe. Il ne sait pas le truc, quoi ! Bouliner sa limace et faucher ses empaffes pour maquiller une tortouse, caler des boulins aux lourdes, braser des faffes, maquiller des caroubles, faucher les durs, balancer sa tortouse dehors, se planquer, se camouffler, il faut être mariol ! Le vieux n’aura pas pu, il ne sait pas goupiner !
In Hugo's plain French translation:
Spoiler:
What are you yammering on about? The innkeeper wasn’t able to make a break for it. He hasn’t got the knack, end of story! Rip up his shirt and carve up his sheets to twist himself a hangman’s friend, belt a few portholes in the door, cook up some false dog tags, knock up a few open sesames, snip his fetters, chuck his twister outside, lie low, keep under cover, you’ve got to be smart to last! The old bugger can’t ’a been up to it, he doesn’t know how to use the old elbow grease!
English
What are you talking about? The innkeeper wasn't able to escape. He simply doesn't have the skill. Tear his shirt and cut his sheets to make a rope, make holes in the door, make false papers/ID, make false keys, break his irons, hang his rope outside, hide, disguise himself, you have to be smart to live! The old man couldn't have done it, he doesn't know how to work!
I'm going to try and post a Yorkish version in a bit.