One large mark against building this feature is that machine translation is still largely worthless. I barely see the point.

Aligning paragraphs in a translated copy would be more useful from a language learning perspective, though generally something beginners overvalue.

Side by side UI also limits you to larger displays unless you will settle for tiny text.

> Aligning paragraphs in a translated copy would be more useful from a language learning perspective

This is exactly the intended use.

ANY help when learning a new language is welcome. Also, the translation quality varies a lot between language pairs. Sometimes it is greatly improved just by removing English from the equation.