This import worries me a bit.  As I described in the app dependencies (linked below), `i18n` references `main` (and vice verse).  There's no current reference in `i18n/__init__.py` to `main`, but we should probably put a comment in there to make sure it doesn't get added, until the refactoring suggested below happens.

https://github.com/learningequality/ka-lite/wiki/Intended-app-dependencies