I myself didn't know that "il lenzuolo" (as a masculine singular noun) is an irregular noun, although I have been familiar with the concept much before. Yes, unfortunately, there is such a unique case in Italian, which is annoyingly hilarious, in my opinion. The other common examples, in case you want to know, are:
il braccio - le braccia (arm - arms), il labbro - le labbra (lip - lips) -- for more info: http://www.wordreference.com/iten/labbro
il ciglio - le ciglia (eyelash - eyelashes), il ginocchio - le ginocchia (knee - knees) -- for more info: http://www.wordreference.com/iten/ginocchio
For those who are interested in further knowledge, these are some websites about irregular nouns in Italian:
http://it.wikipedia.org/wiki/Plurali_irregolari (which gives an astonishingly profound information about the irregular nouns, explaining the origins and the why's.)
I've studied both in school. Each has its own difficulties for native English speakers. German has simpler verb conjugations than Italian and many words that are the same or similar to English. However, German also has a more complex collection of articles and adjective endings, based on three grammatical genders and the nominative, accusative, or dative case.
"Lenzuolo" m.s. (bedsheet -considered as one of the two element of the bedsheet set). "Lenzuoli" m.pl. (Bedsheets -considered as several bedsheets regardless of being part of the bedsheet set or not). Lenzuola f.p. (Bedsheets - Considered as the pair, the bedsheet set).
I can say: Un paio di lenzuola è composto di due linzuoli: un linzuolo è collocato direttamente sul materasso per coprirlo. I'altro linzuolo è colocato sul primo però questo ultimo è per copire il letto completo.
The bedsheets set is compound of two bedsheets. A bedsheet is placed on the matress to cover it. The other bedsheet is placed over the first one but this last one is to cover the whole bed.
- singular il lenzuolo = the (bed)sheet
- plural le lenzuola = the (bed)sheets
This is one of those irregular Italian nouns that change gender in the plural. (gender bender nouns :P)
English uses a single word (sheet) for bed linen and for any piece of material. Other languages use a single word for (paper) sheet and leaf. In Italian they have all three:
- lenzuolo m (lenzuoli m, lenzuola f) = bedsheet
- foglio m (fogli) = (paper) sheet
- foglia f (foglie) = leaf
Ma le vostre spegazioni non sono complete. Vedete qui: http://www.treccani.it/enciclopedia/lenzuoli-o-lenzuola_(La_grammatica_italiana)/
Actually, "linens" does exist in English, as a colloquial usage, although the OED does not recognize the plural form. It might be used correctly to identify several SETS of sheets that are lying on the bed, and it will surely be seen in the linen departments of stores for the same reason. Best English is "sheets" or "bedsheets."
I don't really know about the translation from Italian, but the English term is "bed linen". There is no such thing as the plural "bed linens" in normal usage as the term "linen"is a collective term that refers to all bed linen items. Also, "bed linen" refers to all cotton goods (or similar) used on the bed, not just the sheets. So you could have been marked wrong for either reason I suppose depending on what DL was looking for.