Jargon

Originally this seems to have been the Druidic language. But it is like a somehow hollow fascimilie. It uses some of the words, but it doesn't have the depth of poetry that Druidic relies on. There is a whole other layer of communication that the Jargon misses. So anyone who speaks Druidic will be able to understand Jargon, but Druidic speakers still keep their secrets when they communicate in druidic and they can only be as understood as they wish to be.
Official proceedings of the Unders Ecological Institute are held in Jargon and their main publication Ecologist's Quarterly has been published exclusively in Jargon up until 498.