One of the many ways in which English differs from other languages is its use of uncountable nouns to talk about collections of objects: as well as never being used in the plural, they’re never used with a or an. Examples are furniture (plural in German and many other languages), cutlery (plural in Italian), and information (plural in French). They’re all marked U in the dictionary. They can be made countable, but they need the addition of another word: pieces of furniture, items of cutlery.
One group of words, including some that are new to the Cambridge dictionary, is slightly problematic. Mostly borrowed from Latin, these words are grammatically plural in their original language. Not having a plural –s to show that they’re plural, though, they are reinterpreted as singular (most of us are not fluent in Latin). A very careful speaker will use a plural verb with these words, but plenty of evidence can be found online for their use with singular verbs.
A writer’s juvenilia can be defined as “work produced by an artist when he or she was young”. In Latin juvenilia means “youthful things”. Regalia means “royal things”. Memorabilia means “memorable things”. All of these tend to be seen as “stuff” in English, rather than objects that can be counted. Another “stuff” word is paraphernalia, originally “things owned by a married woman”, and now just meaning “stuff”:
We sell pots, gloves, seeds, and other gardening paraphernalia.
Another group of words ends in –ana. Well established examples are Americana and Victoriana, meaning respectively “American things” and “Victorian things”. They refer to objects, especially antiques, that are seen as very typical of their period. The ending can be applied to a wide variety of words and names, though, to mean objects that are associated with a particular place or person, for example Shakespeareana, stuff connected with Shakespeare, and Potteriana, stuff connected with Harry Potter. This group is usually treated as singular.
Sometimes more technical uses keep the plural use: graffiti is plural in Italian, and archaeologists treat it as a plural in English (for example when referring to those graffiti from Pompeii), but in general usage in English it is almost always uncountable.
Another problematic word is bacteria. A Latin plural, the singular is bacterium. But this singular is used less often in English than would be expected; instead, the –a ending is interpreted as a singular Latin ending, like toga, and can be made plural by adding –s: bacterias. These usages, though increasingly common, are generally not approved of in formal writing.
One group of words that would sound very odd as a plural are the Italian pasta words. Plural in Italian, they are always singular in English, to the horror of Italians. Where Italians might ask “Are the spaghetti cooked?”, standard English has:
Is the spaghetti cooked?
And in similar fashion, panini (which means “bread rolls” in Italian) is treated as singular in English, and even has a plural paninis:
We ordered two ham paninis.
Bad Italian, but good English.