The “Copiale Cipher” is a 105 pages manuscript containing all in all around 75 000 characters. Beautifully bound in green and gold brocade paper, written on high quality paper with two different watermarks, the manuscript can be dated back to 1760-1780. Apart from what is obviously an owner's mark (“Philipp 1866”) and a note in the end of the last page (“Copiales 3”), the manuscript is completely encoded. The cipher employed consists of 90 different characters, comprising all from Roman and Greek letters, to diacritics and abstract symbols. Catchwords (preview fragments) of one to three or four characters are written at the bottom of left–hand pages.Kevin Knight, Beáta Megyesi and Christiane Schaefer (2011), The Copiale Cipher. ACL Workshop on Building and Using Comparable Corpora (BUCC).
The New York Times has an article:
A team of linguists applied statistics-based techniques to translate one of the most stubborn of codes, a German mix of letters and symbols.
While the Copiale Cipher website at Uupsala University's Department of Linguistics and Philology has everything you need to know, here's the direct link to the English language translation (as a PDF).
The contents of the document are particularly interesting, referring as they do to n 18th century secret society known as an "oculist order" - oculist coming from the Greek and referring to eyes...here's the obligatory link to Wikipedia about ophthalmology.