open repository list at https://github.com/diglossa. For example, "The Story of My Misfortunes" by Petrus Abaelardus has repository at address https://github.com/diglossa/Abelard-Historia-Calamitatum
Fork it. Make corrections or add new translation files (for all or several parts of a book), modeled on the existing books.
Each paragraph of the translation have to be in parallel with paragraph of a source text. It is desirable to have each sentence in the paragraph in parallel with sentence of a souce, but this does not necessarily.
Translation's file has a name as part_N.lang.nic, ex. Chapter_01.ru.sokolov. Nic should be described in contents file.
To add a new book from scratch, create among other files a file with contents of a book with extention .yml or .json, look in existing books.
Then send me a pull-request