Latin

We all didn't like the guts in this man, if he had any.
"I've half a mind to kick the lot of you out!" His head snapped round most grotesquely, "Or even better, loot the money from your corpses myself!"
Sergei gave an amiable shrug, "Quam brutum. Non curae," and stabbed him in the thigh.

Latin used to be a prominent language before the founding of Camelot. Soon it became a tongue associated with magic and witchcraft - the language that cursed people's children and spoiled their crops. The vernacular moved on and so did the people of Poraile. Speaking the language publicly became a punishable offence under "Negligent Use of Magic" without even asking whether the offender could use it.
It is the language of the obscure and occult, left to the people it came from. Wiccan, Wizards and wraiths use it to communicate, unnoticed by their nations and authorities. Latin is now the language of the wizards, often overlooked by Alliance authorities as pure nonsense. 
If Latin communications are discovered, the offender is brought against the Arcane Tribunal, where witnesses testify to the harm caused by anyone who recites words from this dark tongue. Punishments vary wildly, but if a defendant survives this public assault of their character, wizard and wiccan communities almost always exile those caught. As far as they're concerned, their knowledge was leaked to the public, who have neither restraint nor understanding. 
Wraiths fare better from this deal, since they mostly reside in the Kingdom of Garka, outside of alliance influence. Wraithfarers have to keep their language to themselves, else alarm the locals and bring about their second deaths. Wraiths that aren't found in time are left bewildered by rampant persecution, unaware that even speaking the tongue of their masters and ancestors betrays them.
In its age of prominence, it was used regularly in church sermons and religious texts. Nowadays, monasteries and nunneries keep it alive in their manuscripts and through business dealings with wizards. Their most valued texts are still in Latin, though a local priest would need to translate to their congregation, else face accusations.

Writing System

Though the language has been forbidden, its alphabet is still used in modern languages that took its place. Any risks of it being too accessible are quashed by the words themselves seeming utter nonsense.
The Latin alphabet has 23 letters, the letter I taking the places of I, J and V. The letter V also takes the place of V, U and W.

Geographical Distribution

It's mostly prevalent in the southern regions of Poraile, spoken only by those who have business with Wiccan. Its spread has decreased since the regulation of magic, since it marks the magical from the aether-ignorant in human cultures.

Spoken by

• Mage
• Wiccan
• Wizard
• Wraith