We came to a point where one of my teammates cast Comprehend languages, but I still spoke in Druidic (actually just for the lolz, but it still raised the question):
Does Comprehend languages allow the target of the spell to understand secret languages such as Druidic?
We have three different things to look at here.
Comprehend Languages says...
For the duration, you understand the literal meaning of any spoken language that you hear.
It goes on to talk about written messages, but this is all we have for spoken language.
Druidic says...
You know Druidic, the secret language of druids. You can speak the language and use it to leave hidden messages.
Again, this is all we have for the spoken language. It outlines rules for noticing hidden written druidic messages and specifically mentions magic being useful for understanding hidden writtings... assuming you notice the message to begin with.
In any case, it's pretty clear that Comprehend Languages helps with spoken Druidic. There's no coding or encryption to make what the speaker says carry anything other than "literal meaning".
Druidic is only a "secret" because they don't tell other people about it. However, it's kinda like Fight Club - it's only a secret because the rules make it a secret, security by obscurity. There's nothing beyond the game rules that make it so.
Thieves' Cant says...
During your rogue training you learned thieves’ cant, a secret mix of dialect, jargon, and code that allows you to hide messages in seemingly normal conversation. Only another creature that knows thieves’ cant understands such messages. It takes four times longer to convey such a message than it does to speak the same idea plainly.
Thieves' Cant is different. It isn't really a language at all - it's a system of coding hidden messages inside another language. Nobody speaks Thieves' Cant by itself.
Comprehend Languages specifically says "literal meaning" of the spoken words. Which means it wouldn't work with Thieves' Cant, as Thieves' Cant is all about coding a secret message within the literal message spoken. The literal meaning and the actual meaning are not the same thing, it's steganography.
Comprehend Languages works on Druidic, but not Thieves' Cant because Thieves' Cant isn't actually a language.
The spell says:
For the duration, you understand the literal meaning of any spoken language that you hear.
Also:
This spell doesn’t decode secret messages in a text or a glyph, such as an arcane sigil, that isn’t part of a written language.
It means that he understand the secret language druidic or any other normally, but can't understand a codified message like "She Almost Got Enlightened" only getting the literal meaning nor understand magical gibberish of glyphs that are not languages (those that look like but are symbols).
Druidic is a secret language also because of how the language is communicated. I place a piece of barley wrapped in a maple leaf on the NE side of a elm tree. I just left a clear message in the druidic language. The spoken language is no more easy to understand as they will use words and sounds from Sylvan and other common natural languages but in combinations that make sense to druids (possibly also including some small emphasis on body language since as a basic ability druids can shape shift so you don't have to worry about non-human druids not having the body parts to convey a message). "Dark are the clouds above the hawks' journey to the sea." I just told another druid in our cryptic language that there is an army marching from the west to make war.
Most "secret" languages aren't translated by Comprehend languages because you will understand a Literal meaning of a message and miss everything else (all the sub-text and codes) that goes with it. It is however a great way to give misinformation to players and lead into adventure plots.
For a potent example of this watch: Star Trek the next generation Season 5 episode 2 "Darmok". Star trek has a Universal Translator (Aka comprehend languages) that is heavily relied upon... But just because know the words the meanings and usage may still cause confusion if not also understood.
"Temba his arms open" ... "Shaka when the walls fell"
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Commented
Jul 26, 2018 at 3:15