I want to point you to a lecture on iTunes U which has the lengthy title From Early Judeo-Iranian Jargons to Central Asiatic Argots of Rom Groups: Evidence for an Influential Jewish Underworld in the Late Abbasid Period. Martin Schwartz (Berkeley) spoke at UCLA about his research into the language of beggars and criminals of Central Asia as can be found in late medieval sources and which has traces until today. The lecture was published in the series from the Center for Near Eastern Studies (feed).
Schwartz's research is mostly linguistic, but since it uses Arabic and Persian sources from the 10th to the 14th century it becomes historic research already by virtue of that. In addition, once he delves into the linguistic peculiarities of his subject, you also get an indicator of historic influences and social stratifications. It seems almost impossible and not serious to research the underworld languages of beggars and thieves, but apart from the fact that there are sources, it always serves looking at society from below, while regular historiography most of the time takes on the top of society.
To be sure, the beggars and thieves do speak the common languages of their environment, whether it is Arabic, Persian or Turkic languages. Yet they have a need for switching to a slang of their own in order not to be understood in the environment when they need to. Strictly their colloquial is not a language but rather a jargon or an argot as Schwartz calls it. What is striking is that they look for replacement words that cannot easily be understood and often find them in Hebrew or Aramaic even if the speakers themselves are not Jewish.
More from the Center of Near Eastern Studies:
Jonathan Mark Kenoyer on Indus Valley Civilization.