About two years ago, I ran a 5e campaign with the following premise: some demigod tyrant of a king has found a passage into the Underworld and is sending anyone he can recruit down into it to map the place and bring back cthonic treasures, wisdom from undead sages, unfinished works from ghostly musicians and so on and so forth. Hexcrawl in Hades.
This post is (mostly) not about that campaign. Instead, it's an answer to this month's RPG Blog Carnival, for whom the theme is linguistics. One of the points where my version of 5e deviates from the standard version of 5e is that I like to curate a special list of languages for each campaign. For the Underworld campaign, that took the form of this chart:
The key phrase here is 'mutually intelligible'. Any two languages connected by a line can be imperfectly understood by a speaker of the other language. If you speak Common, you can get the gist of anything said in Classical and vice versa. Arrows mean a one way connection - if you known Sylvan you can understand what wild beasts are trying to tell you, but the beasts can't understand what you are trying to tell them.
The Divine languages (Titanic, Ouranic, Thalassic and Cthonic) are all mutually intelligible. The Gods of Olympus may not talk to the Gods of the Underworld very often, but they can reliably talk to one another. Instead of having a written form, they can be communicated via omen. The will of Olympus is written in the clouds and the flight of birds, get yourself a priest who can read it for you. Given that the players knew that they were going into the Underworld by dint of the name of the campaign, Cthonic ended up being a very obvious and popular pick, balanced by the fact that its written from was entrails. If you want advice from the powers of the Underworld, you have to bring a live animal along for the trek through this maddening ghost cave until such time as you're looking to consult those Cthonic powers. The Titanic doesn't let you read omens, but it does let you interpret the standing orders of the ancient Clockwork soldiers left behind by the Telekhines. If you had the proper articles of authority you could even give them new orders, if you knew the right words to say.
Beast, Bird, Bug, Fish and Reptile are spoken by wild animals of the appropriate sorts. In the version of mythology I went with, Prometheus (and his lesser known brother Epimethus) were in charge of assigning natural abilities to the wild animals back during the days of the Titans. They were the ones that decided to give wings to the birds, arms to the apes, gills to the fish and so on and so forth. If an animal is particularly weird looking, it gets blamed on Prometheus. What a slacker, giving the ostrich's wings to the bat and the snake's legs to the millipede. (Never mind that a ostrich that could carry people off or snakes with a hundred legs would be horrific and that Prometheus did us a favor by preventing that.)
As a consequence, anyone who speaks Giant can be understood by wild animals of every sort. In a normal campaign this would be pretty busted, but remember: it's the Underworld. Not exactly a lot of wild animals down in Hades to have a chat with. The ones you did want to talk to probably spoke something else as well. Other languages had a similar effect for a narrower range of animals. Cthonic let you be understood by creepy crawlies, Sylvan let you be understood by wild mammals, Thalassic would let you play Aquaman to any fish you encountered.
Common and Classical are Greek and Ancient Greek respectively. Are there non-Greek people in the Underworld? Definitely. Do they still speak Greek? For the purposes of this story, yes. Is that historically accurate? No. But it's how language works in mythology, so that's what I'm going with. The living get to speak Common for free, while antique ghosts speak Classical. The 5e Thieves' Cant ability, meanwhile, would have been altered to cover any sort of secret code or cipher. Assuming anyone had chosen to play a Rogue, which nobody did. But it was on the list in case anyone had wanted to.
Gallic is the shared language of every sort of half-bird creature in the Underworld. Harpies, sphinxes, manticores, sirens, gryphons, pegasi, hippogryphs, flying snakes, you name it. Anything that came from a different mediterranean mythology got put down as being Gallic, including the language's namesake: the galla. AKA bird-headed demons who guarded the ancient Sumerian Underworld. This in turn let me use various demons and devils from the Monster Manual by simply giving them a bird's head and saying that they're a hideous Underworld guardian of some sort. In-universe, Gallic has the same relationship to Bird as Classical has to Common, having once been spoken by an ancient race of birdmen who were to modern birds as Humanity is to modern monkeys.
Sylvan is the language of nymphs, dryads, naiads, lampads and all the dozens of other demi-divine nature goddesses in mythology. Also: Satyrs. It would be fairly boring box-ticking addition to the languages list if not for two facts: First, it's understandable by anyone who is Drunk. You cannot become fluent
in Drunk, but if you get sufficiently intoxicated, you can converse to
anyone or anything that is similarly sloshed. Anything. Get drunk enough with your horse and the two of you can have a
conversation that you won't remember once you're sober. Pour a libation
out in front of a door and the door will be able to understand Common
until it sobers up. What did you think that bottle of sacred wine was
for? In Vino Veritas; praise Dionysus for this miracle.
Second, you can't learn Sylvan unless you are faithfully married to a native
speaker, ie. an oread or a hesperide or something. As you might imagine,
this is something of a Catch-22, because in order to get married to a
neriad, you're probably going to need to be able to talk to her for at
least long enough to propose. This means that you can't parley with the satyrs until you party with the satyrs. Ditto for getting married to a nymph. You know that and they know that and you both know that the other knows it. So if someone wants to make peace, they'll offer up a wineskin. Everyone gets absolutely hammered and has a party. When you wake back up, an agreement has been struck. You might need to piece together what exactly that agreement was after the fact, but there will be some sort of agreement.
