The 40th anniversary edition of Codex Seraphinianus
Huhm, the one that came to mind for me is <i><blue>House</blue> of Leaves</i>, though I guess it's only 21 years old.  It's (almost) fully legible English, but the pages are all sorts of messed up: Text goes forward, backward, sideways, meanders outside standard directions (including through the page), the footnotes span multiple pages and have their own multiple-page footnotes (all telling multiple storylines in parallel) (also one of the footnotes is editing the book as you read it), there's one section written in a simplistic code...<p>There's some pictures of the pages of this book in these reviews:<p><a href="http://www.cornerfolds.com/2014/08/book-review-house-of-leaves-by-mark-z.html" rel="nofollow">http://www.cornerfolds.com/2014/08/book-review-house-of-leav...</a><p><a href="https://stingingfly.org/2016/11/01/house-leaves-mark-z-danielewski/" rel="nofollow">https://stingingfly.org/2016/11/01/house-leaves-mark-z-danie...</a><p><a href="https://www.horrorbuzz.com/2015/09/13/house-of-leaves/#" rel="nofollow">https://www.horrorbuzz.com/2015/09/13/house-of-leaves/#</a><p><a href="http://www.thefeedbacksociety.com/television/house-of-leaves-the-screenplay/" rel="nofollow">http://www.thefeedbacksociety.com/television/house-of-leaves...</a>