How do you go about making a langpack?

Is there a guide somewhere to making a new Ubuntu langpack, one that isn’t mainstream and that can live in your PPA?  Someone asked me whether such a thing could be built for en@shaw (i.e. English written in the Shavian alphabet), and since I have tools which can convert .po files automatically I can’t see why it’d be a problem.  I don’t think Launchpad will ever want to support en@shaw as such, but I can’t see a guide anywhere to building these things– it’s clearly more than just sticking .mo files in a .deb, because something needs to create the locale and so on.  There must be some standard way!