Jelly is another of these words that means different things in different versions of English. Jelly in English English means a large bowl of wiggly stuff (originally made with gelatine) for children to have at parties.
While I think "marmalade" should be an accepted translation for "marmellata" (if it isn't already), "marmalade" in English is actually a narrower type of food, as it only refers to jams made from citrus :)
I wish DL would provide an option to learn the language in either British English or American English. It's becoming increasingly annoying having to remember how Americans speak, but thank heavens for Hollywood.
It's best if duo just accepts both and you also learn both. In my country only British English is taught because it is in Europe, but I still think that knowing how Americans speak would be a nice bonus.
I'm not sure I'd want to learn Portuguese from Portugal and Brazil at the same time, or Spanish from Spain and Latin America, etc. I think it would get confusing trying to separate which words and phrases to use in each country.