@jens92:
Daisy offers a
free Windows ePub to ePub3 Audiobook converter that allows you to convert ePub2 books to ePub3 books with embedded audio files.
The generated ePub3 books can be "read" with iBooks, the Android/iOS versions of Menestrello and Readium.
However, the interface of the Tobi app is rather confusing, to put it mildly. In order to be able to use it, you'd obviously also have to install a suitable Russian TTS voice.
I tested it some time ago and generated
a sample file with English, French and German audio segments.
If you have advanced technical skills you could also use the
Icarus Sigil plugin provided by the developer of Menestrello, Alberto Pettarin (
AiPe), and generate your own ePub3 audio book from Librivox files.