There do seem to be several editions, including a Penguin Classics one (as "The Manuscript Found in Saragossa"
, but yeah, as I said, don't think I'd ever heard of it before, and it caught my eye quite by accident this time (in fact I glanced over its back cover while looking at other books, reading the blurbs without having seen the title, and then was curious which book it could be that was considered so influential for Borges, Eco etc. - I did figure before turning the book around that I'd at least have heard of it!). Amazon.fr's blurb does make the first version sound interesting as well:
En 2002, Dominique Triaire et François Rosset, deux chercheurs lancés sur les traces de l'excentrique comte polonais Jean Potocki, découvrent six manuscrits mal classés dans les archives de Poznan (Pologne). L'étude minutieuse de ces documents leur permet d'établir un fait incroyable : il n'existe pas une, mais deux versions au moins du Manuscrit trouvé à Saragosse. Cette œuvre culte, écrite en français, fut longtemps considérée comme un joyau de la littérature fantastique, et fascina des générations d'écrivains, des romantiques aux surréalistes. Or nul ne l'a jamais lue que sous une ferme tronquée ou amalgamant, en un patchwork infidèle, les textes d'origine ! Commencé avant 1794, réécrit pendant près de vingt ans jusqu'au suicide de son auteur, le Manuscrit trouvé à Saragosse, d'abord baroque, foisonnant et libertin (version de 1804), fut par la suite entièrement remanié et achevé sous une forme plus sérieuse et encyclopédique (version de 1810). Le double chef-d'œuvre de Potocki, près de deux siècles plus tard, peut enfin être lu.
That's what i tried to describe from memory. There are many more interesting details in the introduction. I'm not sure how "influential" to Eco I would place the book, I can't recall an interview or essay where he mentioned it., but I might have forgotten. It's certainly a book that, given his tastes and pet obsessions, he must love. It's hard to tell if it influenced him, though, beside maybe while he wrote Foucault's Pendulum. It's a book I heard of when I was reading a lot of Jarry, Lautréamont, Breton, Mac Orlan, and the pataphysicians like Queneau and Vian. I reread it when I saw that new edition. Mine is a boxset, by the way. All other versions would be of the old innacurate text, including most likely all the current translations.
*NM*