I wanted to work on a similar idea recently for my personal use, but I wanted to use books and stories that already have the texts in the two languages that I am interested in (e.g. Harry Potter).

So you pass in two texts and get back some form of aligned text. If you have some knowledge of the language you are trying to learn and are ok without a perfect sentence-to-sentence alignment, then this would work.

My motivation is to improve my wife's and my knowledge of each other's languages while reading books to our daughter.

For a moment I got excited that someone else had already built it :)