I am a huge fan of the Voynich Manuscripts from early Renaissance that is written in a mysterious invented language with astronishing botanical, sea world, round bellied women floating in celestial arteries and seeming to connect the creative forces of the world. But I also am a fan of this contemporary Codex Serphinianus by the Italian artist Luigi Serafini, who also invented a language and a script he felt would be suitable for describing in text the imaginary world of his art -- rich and transforming, sometimes humorus and ironic, sly, and caught between the modern world and an endless fantastic one. Here is a video in which he talks about his work -- with just a hint of explanation. (And here is an interview with Luigi Serafini at Wired, that is also fascinating. )
And here are more of the illustrations from the Codex -- and while Serafini has many that revolve around a contemporary world infused with fantastic nature, I will say that I love his imagery of a unique and fecund natural world.