@poxalew: Amazon introduced automatic hyphenation support for
Russian language AZW3 books with the 5.6.1 Kindle PW2 firmware update. (First reported by
EbokJunkie in
this post.)
I.e., current eInk Kindle models already have built-in hyphenation support, which has been disabled for all languages, except for Russian.
You can easily see this in my test file, which doesn't contain soft hyphens.