To expound just a bit on his last point...Thieves' Cant is not a language. It is the skill to hide secret messages in whatever language you are currently speaking, so that it sounds like you're just making small talk or whatever, while actually communicating something completely different. It is, likewise, the skill to understand someone else when they are doing the same thing. This could theoretically be learned separate from the class...but so could other things like a Battlemaster's ability to assess a target's skills. So, would require special DM permission

In re your custom background point at the end, linking it to "criminal" background would seem a thematic fit ...

I honestly think that 3.X handled Thieves' Cant "correctly", treated it as a skill, which it is. Never made sense that an elf thief can communicate with the Kuo-Toa thief without an actual language in common. Oh well.

@slagmoth I don't think anybody is saying they can communicate without a common language. It is the ability to hide messages in otherwise normal seeming sentences, this would require understanding of the language being used. The pictographic symbols however could be universalized

Equivocating official with AL-Legal seems misleading. There are many official rules that are AL-illegal.

@DavidCoffron what exactly makes them "official"?

@Medix2 Maybe, but is alluded. And I still have a very hard time believing that the elf rogue and the kua-toa rogue would have any universal writing to share as well. Personally, I treat TC like 3.X it is double talk and there is no special writing involved. A rogue from one city will have to take some time to learn the context and such in a city before they can communicate effectively. Darmok with arms open or Shaka when the walls fell.

@Enkryptor Related on what counts as "official": rpg.stackexchange.com/questions/84836/…

Is thieves cant in any way similar to Druidic?

@Tiggerous afaik Druidic is a language, while T.C. is not

@Medix2 following this logic, custom background features are 100% official, since they are mentioned in the PHB

@enkryptor Correct; custom background features are official; any individual custom background features are not as they are GM coordinated, but having one is officially sanctioned by the rules

@enkryptor the answer there has a whopping 102 upvotes. It is clearly a VERY agreed upon answer, so if you disagree with it that's alright but not how most people see it

@enkryptor Just as a brief note, I think that your disagreements come from the fact that "official" has many meanings and WotC uses and abuses those definitions to the point that currently "official" has really no significant agreed upon meaning.

For example, it could mean "published by WotC" except there are "official" 1st party things that aren't allowed in "official" AL play. It could mean "supported by the core rules" which would mean that some of the things you mention would indeed be official. It could mean endorsed by a WotC employee (in the way that the Sage Advice Compendium is "official" guidance).

Personally, I avoid using the word and instead try to be more specific as to what I mean by it.

@Rubiksmoose that wasn't a disagreement. "official" has many meanings indeed. I've just asked DavidCoffron, what did he mean. Don't know why did this draw so much attention from other people.

@enkryptor Eh, it's just one of the things that annoys me. Sorry if I read disagreement where there was none.

(and it was in no way chiding to you or anyone else involved)

So feel free to disregard my mini-rant :)