Dekken is a secret language, used by the criminal underworld all over Mithra. The language secret code made from the rules and words of the Common tongue. It is used in the criminal underworld, by thieves, highwaymen, assassin guilds, and other criminal scum. It is quite easy to learn but there are no books on it (until now), so learning it is almost impossible if you are not in active in the underworld. The language evolved into its own thing, making it a separate language and not just a cipher from the common tongue.
Today's Dekken is the third iteration of the language. Twice in the second era, Dekken has been invented. Both times, it was lost to time. This also has to do with the fact that it was outlawed in the empire, making learning and using it extremely dangerous. By the end of the third era, a new Dekken was invented after someone (we don't know this bit for certain since none of this was written down) found a book that detailed the old Dekken. Whatever it was that brought new life to Dekken, it worked. Dekken is now spoken by almost 80% of all criminals. It started, like every time, off as a cipher for the common tongue. The cipher was used to change common words into Dekken words. This was a language on itself though and evolved separately from the common tongue. This made for new words, grammar rules, etc, until it was a real language on itself. It mostly evolved in the underworld of Lakaath
, one of the most criminally active cities in the Republic
. The massive citern houses so many criminals that it is almost exclusively spoken there these days. This is the place where i learned it too, a few hundred years ago.