Languages

 Languages are often underutilized in OSR, while I believe that they were used extensively in early editions of the game. This is probably due to people not understanding why they are there.

In the base game you roll for reaction when you meet monsters. Only on a 2 do they immediately attack. Otherwise you have some opportunity of talking to them and potentially reaching some mutual agreement.

But not all intelligent monsters speak human language. Instead, they all have special languages of their race.

Hobgoblins speak hobgoblin. Goblins speak goblin. Giants speak giant. Lammasu speak Lammasu.

Early d&d didn't care about approximating real life. It was a game, for fun. Certain concessions were made.

So, why does every monster have it's own language? And what's the deal with alignment languages?

Each monster has a language so players can parlay better with them, while making interactions with monsters they didn't share a language with more difficult and dangerous.

It leans a little bit into skilled play at character creation. What monsters do you want to parlay with? Do you pick the dangerous ones, the helpful ones, the common ones?

Alignment languages is a fail-safe. I think if it like native American sign language - a shared tongue capable of identifying friend or foe and discussing basic concepts. Speaking neutral with lizardmen might get you a few basic directions or confusion. Also, you can't lie in alignment, which is why you can only learn one 

Here's the languages in my campaign

Trade-common : known by all Domzweleki

Sacred Imperial : language of the old empire

Faerie : language of goblins, elves, and dwarves

Wild Wood : tongue of witches, barbarians,  and wild men

Celestial : angelic beings, lingua franca of Cult of Dawnbringer

Infernal : daemons

Black Tongue : a fell language spoken by crows, spiders, and humanoids

Tinker’s Cant : trade tongue of beggars and thieves

Alchemist’s Cant : trade tongue of petty sorcerers

Tongue of beasts : cost 2 languages

Tongue of birds : cost 2 languages

Tongue of fish : cost 2 languages

Tongue of vermin : cost 2 languages

Wyrmish : spoken by dragons, worms, naga, and serpents. Cost 2 languages.