I notice that https://wikimania2015.wikimedia.org/w/index.php?title=Hackathon&veaction=edit&vesection=7 contains a lot of exposed <translate> and <tvar> markup.
It would be nice to support this properly in Parsoid (and eventually Visual Editor as well, but let's start with Parsoid).
IIRC, the markup for the translate extension is not particularly complicated to parse. Much easier than Language Converter, at least. The hard part is probably figuring out how to structure extensions in Parsoid, but we can deal with that as a refactor once the basic functionality is implemented.
This seems like it would be a thematic and appropriate Wikimania hackathon project.