Book translating and publishing seems like a thriving business now in BD, many making a living out of it. But as like most of all thriving businesses this too has an illegal component in it, which makes people who want to live a honest life not to indulge in it.
For translating and publishing an author's book legally you need to seek permission from the foreign author and his publisher, and send them loyalty for each book printed. It's called copyright.
If that sounds "too much" or "might be legally required, but not ethically" then think what you probably will do when someone else takes your translation and publishes it himself for his profit without talking to you.
Now let me add that some group from the muslims deny "intellectual property right" having any place in Islam. Right now I can think of only one such group, the HT's from the 2000s. And I am not here to oppose them. But even if we accept them for their ruling, the problem of "what if someone republishes my book" lingers. Opposing re-publication of my book, while supporting re-publication of others sounds a bit hypocratic.
I don't look at anyone publishing a book with or without a permission as indulging in a sin. Rather these thoughts are only for those that wonder whether the money I am making is fully clean.
This is another business idea that I see, but can't actually get personally involved in.