Adding Miga to Translatewiki.net
Fragment of a discussion from Support/LiquidThreads
Of course the text must not be hardcoded :) as for the formats you can choose, see mw:Help:Extension:Translate/File format support. JavaScript or JSON are probably what you're looking for. Keep in mind that, if not immediately, at some point you'll want to add plural support too. See for instance Etherpad lite which uses JSON and recently added plural support.
You'll also have to add documentation for the messages and to add @siebrand and @nikerabbit as users with push access. As for a more detailed evaluation, Siebrand or Niklas will check at some point.