I just read Riddley Walker (1980), by Russell Hoban--a post-apocalyptic tale told by the young Riddley in a future-language, of which Hoban says:
"Early on the language began to slide towards Riddleyspeak; I had a lot of fun letting words wear themselves down into new words and new meanings. ... One thing led to another, and the vernacular I ended up with seems entirely plausible to me; language doesn't stand still, and words often carry long-forgotten meanings. Riddleyspeak is only a breaking down and twisting of standard English, so the reader who sounds out the words and uses a little imagination ought to be able to understand it."––From the author's notes, here, where you can actually read the entire novel online.
The people around Riddley want to discover the power of the previous society, which blew itself up in nuclear war two thousand+ years ago, and eventually they discover the secret of making gunpowder: sulfur, coal, and saltpeter.
All screencaps are from "Arena," thanks to Trek Core.com, and all text is from Riddley Walker (mostly from chapters 16 and 17).