Got an idea for a transhuman story element.
Assume that the technology exists to let you acquire fluency in a language of your choice as easily as you install a font on your computer. (Such technology figures in When Gravity Fails and probably bunches of other fiction.)
My idea is a Private Language Generator, which uses some source of true random noise to generate a language — syntax, phonology, morphology, lexicon — from the ground up, and install it using the interface assumed above. When two or more people use the device together, they acquire the ability to communicate ‘naturally’ in a language that no eavesdropper can interpret.
This leads to a new kind of traffic analysis. Any two people who Tweet in the same unknown language thereby expose their association. So maybe the PLG is not all that useful for secrecy. But lovers, for example, might use it for fun. (See also The Languages of Pao.)
I don’t think there’s a need for that. Just use a block-cipher to encode an existing language, with some layer on top that turns the apparently random output of the cipher to pronouncable and handwritable syllables. If you want to communicate to another person this way, you just create the keys with a Diffie-Hellman exchange with your partner, or, if you want to communicate to a whole group people, use a more expensive private key encryption to tell them the key secretly.
Where’s the fun in that?
Real languages have redundancies that compensate for noisy or lossy media; modern encryption destroys such redundancies. A message in the format you describe is meaningless if damaged.
Ideally a generated language should respect the users’ tastes (and auditory or articulatory limitations if any). I’m imagining an unconscious negotiation mediated by the PLG. It would be interesting to see whether typology reflects personality traits.
What would be the scope of the invented vocabulary? Would a word be invented for every concept known to both? Does a secret name for Stockton Street, say, exist (only) in languages whose speakers all know their way around San Francisco? Should my private language have its own code-name for (e.g.) Lana Turner, of whom I know next to nothing?
Should the PLG have a way to update the lexicon for new shared knowledge?