Age of Arthur - Si Vis Pacem, Para Bellum
Excerpt from the main rulebook (pg. 13-14).
“The Fae are spirits of the wild in physical form. They are ageless. They dwell at the wild edges of civilisation in places mankind fears to tread. All Fae are capable of using the form of magic known as glamour to fool the senses and perhaps create more solid things. They are creatures of caprice and illusion. The emotional outlook of a typical Fae, or even a powerful Fae noble, resembles that of a spoiled child.
Paradoxically, the Fae are also creatures of habit. One of the Fae, with a given role in life, will often follow that role for all eternity unless circumstances change. A Fae cannot break his sworn word, doing so causes physical damage, though he will adhere to the letter rather than the spirit of any oath.
The Fae are associated loosely to the seasons of summer and winter. The summer Fae tend to be creatures of light and beauty and are termed the Seelie. By contrast, the dark and terrifying winter Fae are called the Unseelie. The Seelie and Unseelie instinctively war with each other, and sometimes make use of others in their battles. The Seelie will not usually directly harm humans unless insulted or offended.
But be warned, it can take surprisingly little to insult one of the Fae and some are prone to mischief. The Unseelie, by contrast, will often simply hunt down and kill humans who come too close to their territories. While not always hostile, the Unseelie are instinctively malevolent and will choose to harm rather than help others when both options are available.
As a default, the Fae are too alien to be allowed as player characters, though characters with Fae ancestry are perfectly acceptable and may even, though outwardly human, have access to some Fae magic."
The Fae nobility speak Ancient Celtic (in the modern era we call this Proto-Celtic). This is the ancestor of both Brythonic as well as Goedelic and therefore feels familiar enough to drive both cultures batty with words that almost sound like something they recognize, but don’t.
The written system is typically Ogham.
As for names and personal predilections (as well as everyday communication with mortals … if they must); that varies depending on the region in which they find themselves. In an area that’s mostly Breton, it’s one way. An area of Picts, another. Etc. etc.