I have been re-reading lately. I just re-read The Name of The Rose. There will be a spoiler below (warning in case there is anyoneone who hasn't already read "The Name of the Rose"). I have never read "Il Nome della Rosa" but I will object to the translation.
To make space before the Spoiler I note an article by Eco entitled "Il Nome della Cosa" . La Cosa was the name to the organization formerly known as the Communist Party of Italy as they were changing their name. Eco warned the head nameer Achille Ochetto (Achilles Gosling and getting its name from someone named Achilles Gosling is just one of the many things a political movement must do to manage to lose to Silvio Berlusconi). Somewhat redundantly, Humbert Echo warned Achilles Gosling to beware of translation. He noted that calling the party "il Partito di Lavoro," that is the labour party, would reassure Englishmen much more than calling it "Il partito dei lavoratori" or "The Worker's Party."
Of course they chose "The Democratic Party of the Left" just like the East German communists who, quite frankly, seem to have a more promising proximate future (they are now "The Democratic Party" and, I kid you not, appear to be the most disorganised Michiguna organised party with that Florid name (non would have neva[da] guessed).
OK so to "The Name of the Rose". There is a cryptic note which explains how to enter a crypt. In the original it is clearly a pun based on the confusion of a word and the concept for which the word stands (as Plato had two hands and no letters and "Plato" has five letters and no hands) It is mistranslated by William Weaver as
"The first and seventh of four" William of Baskerville and brother Adso think this is an enigma, because a group of four can't have a seventh element. This missinterpretation makes no sense because of the misstranslation. The first and seventh of four things can't exist, nor can the first and seventh of the four, but the first and seventh book cases of room four can exist. In either case a word should be added (not either book case you twit).
Oddly, when Baskerville understands that the unpuncutated note is to be read as "Primum et Septimum de 'Quatuor'" he is translated as saying "does not mean the first and seventh of four, but of the four". This is going backwards -- both "the first and seventh of four" and "the first and seventh of the four" can be miss-interpreted but the correct interpretation is more natural without the "the."
Now I attempt to deduce the Italian. I know no Latin so I will attempt to translate back from English. This is interesting for two reasons. In Italian adgectives havegender and number, which makes it harder to confuse the number 4 (four), the noun which names the number 4 ("four" or "Quattro") and the adjective which distinguishes groups of four from other groups ("four", "quattri" or "quattre"). Also definite articles are used differently and more often in Italian se il mio ricordo e esatto (if the my recollection is correct).
Having been confused by the "the" I thought of "il primo e il settimo dei quattri". This is wrong. It must mean "the first and seventh of four things" and so is impossible not possibly missinterpreted as impossible. Then how about "Il primo e il settimo de quattro." Quattro must be a noun so this misstranslation of a misstranslation can be interpreted as "q" and "o" or as the bookshelves etc.
Finally I guess that Eco probably wrote "Il primo e il settimo de quattri" or, word for word "the first and seventh of four." Duh. Without quotation marks, the word for word translation from English is ambiguous in Italian. Furthermore, four must have been "quattri" because the note refers to a words written on the wall of the library and "Quatuor" is used as an adjective.
I wrote that Eco probably wrote "Il primo e il settimo de quattri" not because I think he may have written something else in Italian, but because he might have left the Latin untranslated. There is quite a bit of Latin in WEaver's translation and quite possibly much more of it was not translated or paraphrased in the original. Italians study Latin in high school, Eco probably had no idea how popular the book would become.