Should you translate everything? Or what?

For my own education and entertainment, I am translating a book of Japanese short stories. Simply deciding on the best English word is a routine challenge. For example, my dictionary often gives several synonyms for a Japanese word. For example, 言い訳する can mean "to make an excuse, to explain, to justify." Those three English words are all similar, but making an excuse is different than explaining or justifying one's action. This means that the translator has to consider the context in which the author has used 言い訳する to begin to approach the Japanese meaning.

In addition to these common decisions, I'm stumbling over what to do about a Japanese word for which there is no English equivalent. At one point, the wife is preparing a bento box lunch for her husband to take to work. She asks, "Do you also want natto?" 

Natto on a bed of rice

I am going to assume that enough Americans have eaten in Japanese restaurants so that they know what a bento box is. But what about natto? How many people who have not been to Japan have tried natto? According to Wikipedia, it's "a traditional Japanese food made from soybeans fermented with Bacillus subtilis var. natto. Some eat it as a breakfast food. Nattō may be an acquired taste because of its powerful smell, strong flavor, and slimy texture." There is, as far as I know (and I like natto), nothing like it in the West, so what is a translator to do?

You don't want to send your reader to Wikipedia in the middle of the story. You don't want to translate the wife's simple question as, "Do you also want soybeans fermented with bacillus subtilis?" 

My solution, which I am not happy with, is to footnote the word: "Fermented soy beans in a sticky web." If this were a book, another answer is to include a glossary at the back. A third approach is to avoid the word entirely and omit the wife's question or have her ask, "Do you also want something on the side?" I'm not happy with any of these and I'd be interested in other thoughts. If you have an opinion, I'd be delighted to hear it.