This is a book created with YouAlign. Only thing you need is a file with the text in language 1 and a file with a text in language 2. The website looks at the content and aligns so that it matches line by line (it's meant for translators, but my main interest is in creating bilingual books). I accidentally tested this because my Italian translation was missing a line, so YouAlign just made the spaces between paragraphs bigger so that the texts would stay aligned on its own.
Files need to be smaller than 1MB (try deleting the covers ebooks sometimes have inside if you're over the limit) but other than that and no locked PDFs, it takes a bunch of formats with no problem. Have only tried Latin script languages, it might have issues alignigning stuff like English and Chinese or Russian and Portuguese, for alll I know. Hopefull not :p
If you want to check out some ready made bilingual ebooks, try Farkas. They even have a program to turn the books into ebooks, something I haven't yet figured out how to do with YouAlign generated files (feel free to enlighten me!)
Hope you find this useful :)