Comment by klakierr

I've built a cli tool to insert translations into an ebook file, converting a standard ebook into a bilingual ebook. I wanted to learn Spanish, and all other learning methods were too boring.

I've made a lot of progress with my Spanish this way (it's fun), so I started to build a language learning app based on the idea, but then decided I do not want to build language learning app, so instead I just added a web UI layer over the tool:

https://bilingualebooks.net

I've just finished it. If you want to use it, note that only DRM-free epub ebooks are supported. Since it's tough to find DRM-free ebooks, especially in foreign languages, I've included a section in the FAQ on where to find them.