OK, this rules — ask and you shall receive.
You can tell the Kindle to show foreign language translations, instead of same-language definitions, with its builtin dictionary feature. This is something I had reason to want, wondered if it were possible, and it turns out that it already exists.
Here’s the background: one of my favorite books in any language is Labyrinths, by Jorge Luis Borges, an English translation of works originally published in Spanish as Ficciones. (OK, that’s an oversimplification — Labyrinths is not exactly a translation of Ficciones; both are collections of short stories, but not exactly the same set of Borges stories. Still, Labyrinths is the preeminent English-language translation of Borges, and it’s a great collection of stories.)
I’ve read the English translations several times (the stories are extremely rich and deeply layered and get better with multiple rereadings), and it’s long been a goal to eventually read them in Spanish, but I don’t know Spanish. Now, however, I’m learning Spanish; also it turns out that Labyrinths is not available for Kindle, but Ficciones is. I figured this was a good excuse to jump in and give it a try.
Once I started reading the stories in Spanish, I found it possible but extremely slow going, as reading in a tentatively acquired foreign language always is. Partly the problem is slowing down and making sure comprehension occurs, and partly it’s vocabulary. Looking up each unfamiliar word in a separate dictionary is really slow and takes you out of the original book, but if you skip too many unfamiliar words without understanding them, it’s hard to understand the overall writing.
Meanwhile, the Kindle has a builtin dictionary lookup feature, where you move the cursor over any word and it shows the definition of the word (at the edge of the screen, and you can push a button to jump to a longer definition). This feature shows English definitions of English words, but driven by the above need to improve my Spanish vocabulary, I started wondering if the Kindle dictionary feature could show me Spanish –> English translations instead of English –> English definitions.
I did a web search for this, and immediately found some questions and answers indicating it is possible — the technique boils down to: buy a dictionary with the translations you want, then from the Home screen’s menu go to Settings, then from the Settings screen’s menu go to Change Primary Dictionary, and select the new dictionary. (This process is nicely documented here, but the dictionaries they link to are in the wrong direction. I bought the Merriam-Webster Spanish-English Translation Dictionary instead.)
It’s not perfectly seamless — you have to pay for a separate dictionary for each language, buy the dictionary ahead of time, tell the Kindle to use it, and only one dictionary is active at a time — but still, I expect this to be immensely helpful both for my reading of Ficciones and for my learning of Spanish overall.