Deep Common
Language of Káto
A language that is widely spoken in the areas known as Káto and the Lost Paths, massive expanses of tunnels and caverns that compose an interconnected world. Speakers of this language come from all walks of life and from many different races but they generally share experiences in the dangerous passageways that make up Káto. The script for Deep Common shares some similarities with Elvish due to the fact that it uses sweeping motions and strokes to write it, many scholars believe that the language evolved from Elvish due to the presence of Silver Elves as an ancient society in Káto.
The earliest appearance of this language is difficult to track and arguments ensue over records as races usually opt to record documents in their native language instead of the shared languages. Undercommon has existed almost as long as the races of Káto have and seems to have emerged as a shared language that can be used for communication and trade. The Deep Common language uses a unique script but the words contain simple sounds that are easy to form and use for most races which makes it widespread among a variety of creatures and races. The most common speakers of this language are Silver Elves, Gem Dwarves, and Deep Fairies but all of them claim to be the actual creator of the script with little to actually substantiate the claim. This language has a large presence in Káto though it will seldom be used unless there is mixed company, while denizens of Káto may speak the language of another it is considered an insult to not use the common language so that nothing can be misunderstood.
The advantages of speaking this language only apply to those that travel and do business in Káto, other places of the world seldom have a use for this language. If you have the ability to read this language then you will gain the ability to trade with races of Káto and garner some respect from them instead of being treated like a clueless outsider. Additionally, some of the strange horrors and monsters that live in Káto have picked up this speech which would allow you to talk your way out of a situation or barter your way through a dangerous area. Dragons that live in Káto also are proficient in this language from the time that they are wyrmlings, speaking this language would go a long way in convincing them that you actually know something about Káto if you are from a race that doesn't make their home in the twisting tunnels.
Writing System
Deep Common Language Letters by Drow Font by Daniel U. Thibault, Chart by RiverFang
Deep Common Language Numbers by Drow Font by Daniel U. Thibault, Chart by RiverFang
Root Languages
I like the idea it's considered rude not to speak Deep Common in mixed company. That's a nice touch.