It is annoying that artificers can't get this. Since if they could then I could do the Hitchhiker's Guide "put a fish in your ear"

Does this spell give you the ability decipher Druidic?

Does “understanding” it allow you to speak the language, or is it just a one-way thing?

Way late, but here. ;) It's just a one way thing. "Comprehending" only. To speak, you'll want the spell Tongues, which is higher level.

Would this spell generally work for a language only a single person knew? Basically I am writing a book for my campaign about primordials and the paranoid npc it was written by used a language of their own design to prevent others from reading it. But it's not a code so much as language that no one else uses. 

Would this trump thieve's cant?

Probably not. Comprehend Languages allows you to understand the "literal meaning". Thieves' Cant uses a combination of alternate meanings of words and phrases, and innuendo. It would be up to the DM whether you understand the alternate meanings of the words. It would not grant you the ability to understand the implied message from the phrasing and innuendo. You'd have to figure that out on your own.

Does this work for messy handwriting, or is that considered more of a cypher?

Can comprehend languages work on Morse Code?

Pretty sure it is not "spoken language".

it is labellled is it shown as as the letter R in a book next to the casting time.

I know my comment is a little nit-picky and I don't want the rules to change but I think that the fact that this spell can't decode secret messages a little funny, because in real life, coded secret messages are easier to decode then figuring out a foreign language.

I kind of know this because of the Code Talkers used WWII who were native Americans and used their native language to help encode messages and the code was never broken.

i’m trying to say stuff with my AutoCorrect because I’m lazy and it keeps messing it up or north of a timer for like a potato you see

Quote from JaCoRo >>

Is it an error that Clerics can't cast Comprehend Languages?
I have a Knowledge domain cleric and realised that there's actually no way for him to read foreign languages! Channel nDivinity: Knowledge of the Ages grants skill/tool proficiency for ten minutes, but I don't think languages a "skill"? (In RAW game terms!)
I was thinking that when he gets into third level spells then Tongues would do it, but that's spoken comprehension only.
Does this seem like a big gap to anyone else? Or am I just a munchkin?

 Nerd

Quote from JaCoRo >>

Is it an error that Clerics can't cast Comprehend Languages?
I have a Knowledge domain cleric and realised that there's actually no way for him to read foreign languages! Channel Divinity: Knowledge of the Ages grants skill/tool proficiency for ten minutes, but I don't think languages a "skill"? (In RAW game terms!)
I was thinking that when he gets into third level spells then Tongues would do it, but that's spoken comprehension only.
Does this seem like a big gap to anyone else? Or am I just a munchkin?

 Nerd

What about druids i’m too lazy to look at this, but can you talk to animals?

Quote from Pineappless890ae2ba09cdf >>

What about druids i’m too lazy to look at this, but can you talk to animals?

This spell doesn't allow you to talk to animals, no. This spell just lets you understand any language that you can hear. Animals don't generally speak languages, so you wouldn't be able to understand them, plus this spell doesn't allow you to speak languages you don't know, just understand when other people speak them.

There is a spell called, very imaginatively, speak with animals that does allow you to speak with animals.

Quote from Edem >>

A lot of people might overlook a very important part of the Comprehend Languages spell. The spell lets you you understand the literal meaning of any spoken language that you hear. Emphasise on literal meaning. While it might not seem very important for someone who only speaks one language, but let me put it this way: for native english speakers, if you hear "tell me about it" after you rant about something, you understand that the listener feels the same way as you, while my first reaction would be to say "but I have just done that, were you not listening?".

 As a neurodivergent person, I need this in real life 🤣

Would this work in a dream? 

Quote from Lambastard_13 >>

Would this work in a dream? 

I don't see why not.

My question about the spell: Does the caster "identify" the language? Like imagine a sign written in orcish. If he casts the spell and on that sign he can read "Only our kind shell enter", does he know that "our kind" must be orcs, or is that a seperate check?