I just think that TC isn't supported as a take-able language with our current language system, not that it's not supported as something we can achieve with the correct rp.
Some language systems show up as a scrambled make believe language with the inflection and "sounds like" the language spoken, while if you have that language you will see the translation in the combat log - if not, you see nothing. (see Arelith's language system.) In this case, Thieves Cant worked alright. Then again, it was all emotes and no words. Like *Blinks twice* and *screws mouth* and other facial gestures and hand signals. Our language system wouldn't support this, since all we get is [LANG] and it's up to us to be responsible gamers and understand or not understand it. So ThC would be a poor choice to implement. Because it would be seriously cheese-sauce.
[ThC] The Garda is coming, did you hide the guns?
[ThC] Yeah, with the explosives. Long live Gundarak!
[Bal] *Eyes the two suspiciously*
But yeah, I mean, speaking in code can and should be developed if you want to talk about plans out in the open or give quick and easy signals to other members of your group. If you think about it, with all the random stuff that get's said IC by outlanders and the like, how easy would it be to start a sort of cypher for your buddies and get away with it? Effort is key.
Kind of reminds me of how we plotted all this secret plan stuff in a hotel room, then left on our way to the plan, and everyone was flailing around "We forgot the plan!" "What?s the plan again?" "THE PLAN HAS CHANGED we're all gonna die!" (you know who you are XD).