I'm currently translating something written in a colloquial style and I'd like to replicate that, but I can't find the necessary words and phrases for that. Are there any resources about that on the internet? Searching both in English and in Esperanto I only found a couple ones here.
I would say it all depends on how colloquial you want/need to be.
To me a key part of being colloquial is to avoid overly complex structures and keep the language simple. Keeping it simple is something I strongly recommend anyway in all cases – after all Esperanto was created to help communication between people of different native languages. So I suggest you to have clear theme-rheme sentences (see the circular letter by Gramatika Sekcio de la Akademio de Esperanto) instead of sentences with lots of loose, nonrestrictive clauses. I would also try to avoid compound verbs ("esti + participo") and to prefer simple verb forms incl. the oni-passive.
The videos by Evildea on Youtube should give you an idea how to be fluent and colloquial in Esperanto.
The article by David Jordan, to which you yourself refer, gives some individual words which add a taste of being colloquial.
By applying the ideas above you should be able to have a casual, colloquial style in the standard Esperanto.
If you need to go further, that is to have slang, jargon, you need to do more. An Esperantist by name Manuel Halvelik (a.k.a. Kamiel Vanhulle) created an Esperanto sociolect triplet (sociolect is a term in sociolinguistics for a non-standard dialect or register used by a certain social group). While one of them is a fictional archaic form of Esperanto (Arcaicam Esperantom), the other two Gavaro and Popido are suitable for more modern contexts. To put it simple, the difference between them is that Gavaro follows more staunchly the Esperanto grammar, but has own vocabulary, while Popido has more radical changes in endings, particles and correlatives (see the linked articles for rules of conversion from the standard Esperanto). However in their extreme form an average Esperantist will have hard times to understand either one of the "dialects", so perhaps some small subset will do the job for you.
ek!. Oni mallongigas en familiara parolado, ĉar ĉiuj iel scias kiel tutigi frazojn, pro tio ke ofte temas pri ĉiutagaĵoj.
diable, kiun mi neniam aŭdis. Se ne estas
Homoj!(kiu rolas kiel
hej!por granda grupo kaj kiun mi aŭdis multajn fojojn).