She hands him the napkins. "The bar is magic and sentient and communicates by conjuring napkins with things written on them."

He reads the napkins. "I would like to know more about the translation magic," he tells the bar.

It is an ambient effect of the establishment not under my control. It optimizes mostly for people who are not paying attention to never notice its presence when possible, although this breaks down in some cases such as the particularly heavy use of puns, sign language with non-signers, etcetera. The most common manifestation to the extent I can expect anyone to report on what they experience to me is that people hear their native or most expected fluent language unless they speak whatever their interlocutor is speaking, wordplay is force-translated, and people who have in fact noticed the translation effect can with some deliberateness manage to communicate about phonemes rather than content by intending to.

"Do you mind if I run a bunch of tests on it?"

Not at all.

"It's a shame Curufinwë's not on this ship," he says - "I want to test what qualifies as a language, so I'm going to speak in constructed ones at various stages of development, Edie, can you tell me whether you can understand me -"

"I can understand you."

He goes through two dozen more of them, a sentence apiece, from conlangs still in the very early notes stage to ones that have a few dozen works written in them.

As long as he isn't making things up on the spot, she can pretty much understand all of it.

And when he starts making things up on the spot, does it matter if he's following pre-established syntax and word forming rules? 

- if he has two conlangs in which the same string of syllables mean different things, and he says the string of syllables, which does she hear -

If he's following pre-existing rules she can still understand him. If he's intending to say things in one or the other language she hears that, if he's focusing on saying both she hears the phonemes.

Signed languages, writing, cyphers -

The translation effect around sign is weird but it works. Writing translates. Ciphers don't.

If she's been taught the cipher -

Nope, she still has to decipher it manually.

What's the operative distinction between a cipher and a constructed language, here are ten test cases where you could make an argument it's either -

...Seems to be intent-based, sort of, it the point of the cipher is to keep people out it'll do that.

Intent of the creator or the speaker - "I need more people here to work with -"

"Anyone in particular, or just people in general?"

"You said you can fork people?"

"Well, Cam's the one who knows the specs for the machine that can turn demon-conjured chip copies into viable ones."

He raises an eyebrow. "Well. That's incredibly dangerous."

"I'm not writing down that it exists even under the strongest cipher possible."

"It means that even if we send Melkor back to Hell, if he ever figures it out -"

"True. But not actually any more true than it was before I found this door. And wasn't the plan to resummon him immediately under the strictest binding possible, rather than leaving him to roam free in Hell?"