Originally Posted by Doitsu
AFAIK, the Kindle offers 7 free monolingual dictionaries (en-US, en-UK, fr, it, de, es, pt-BR), some of which are downloaded on demand, and IIRC other Kindle Fire users reported that they successfully downloaded other English or French dictionaries.
So why don't you humor me and give it a shot. Just sideload my 2 very small test files to your Fire and report what happens if you try to look up the first 4 words.
You may be referring to Kindle or Kindle Touch, which have localized UI for those same languages. And unfortunately these do not support Russian dictionaries (I have tried it on my KT, KK, K2). Apparently many good people have tried unsuccessfully to get it to work. Some issue with mobi, I think it applies to all non Latin scripts.
Amazon is reportedly working on a Japan launch of Kindle, so perhaps as part of this they'll have an update that allows such things to work.
Again Kindle Fire does not have localized UI and there is no way to set a default dictionary. At least mine does not. Maybe the people who report success have rooted and given their Fire supernatural abilities.
And consider yourself humored, I did load the files and dictionary lookup just used the existing (English) dictionary. Cyrillic displays just fine, however.