If you consider making a theme I'd definitely wait for the Smarty change. It should make your life much easier. Getting translations inside the templates is also something we've been talking about when doing the Smarty conversion and it would be pretty easy to implement (there already seems to be a Smarty gettext plugin).
The branch is ready for use, the only thing missing is some serious testing by people other than the ones working on it
Then it could be reintegrated. There's of course other stuff we can and will do on the Smarty side, but the task of converting the templating system 1:1 has been complete for a while now.