Esperanto has a literature (both original and translated) including criminal stories. Criminals are often portrayed as speaking some slang, so my question is:
How does criminal slang looks like in Esperanto?
La sociolekta triopo
Manuel Halvelik created three sociolects for Esperanto, Arcaicam Esperantom (1969), an archaic pre-form of Esperanto, Popido (1973), a constructed dialect of Esperanto, and Gavaro (2006), an argot of Esperanto. Arcaicam Esperantom and Popido are used in the Esperanto literature, but I don't know a work using Gavaro (what is not surprising, looking at the publication date of Gavaro).
An interesting feature of Gavaro are the numerals, they are taken from Volapük and are obscure to Esperanto speakers: 1 bwal, 2 twel, 3 kwil, 4 fwol, 5 lwel, 6 mwel, 7 vwel, 8 zwul, 9 ĵwel, 10 dweg, 100 twum, 1000 mlat.