Yes, mechanical. It's a copyright issue, I cannot offer translated books, so each user upload will get separate generated and inserted translations. Obviously the quality is not the best compared to professional translations. For that you can try beelinguapp.com or lingq.com, both mentioned in this thread. What's different in my app is that it inserts translations in the text, so no additional clicking, and it allows you to upload your own books.

I've tried using LibreTranslate, GoogleTranslate, DeepL, ChatGPT 3.5 and 4 for translations - in my experience ChatGPT is the best for this use case, 3.5 is good enough and economically viable, 4 is superior, especially if you want translation in a language different than English, but expensive compared to 3.5: ~$20 for a book.