After much research, I have come to the conclusion that (1) the only commonly available ereader without out of the box English <-> $language dictionaries is the Kindle, and it's not possible to install additional dictionaries, and (2) my best bet for a number of reasons is probably going to be an Android tablet.
Does anyone know whether there are ereader apps for Android that allow installation of offline English <-> $language dictionaries (I'm interested in Russian, Hungarian, and Swedish particularly, but also French), and whether there are
good offline dictionaries available, ones that don't require you to be able to turn the word into its root form (especially important for Hungarian) and which work within the ereader program without having to leave the book?
I've done some looking around and at one point installed Moon+ Reader on my phone and then failed to figure out how to use any of the supposedly available offline dictionaries, but I haven't really been able to find a clear answer and trying to figure out how to do anything ebook-related on my phone (NOT my preferred reading device) makes me cranky.
It looks like Moon+ Reader and ABBYY Lingvo Dictionaries might be
exactly what I'm looking for, but I can't tell without buying them, so I thought I'd ask if anyone else has successfully used this combo. The ABBYY reviews look like they are expensive if you want to buy the more "advanced" dictionaries and the software may be pretty glitchy.
This is driving me up the wall--it seems like such an incredibly obvious and useful function of ereaders, I'd think everyone would have this kind of feature.