With the feature freeze approaching quickly and plainbox (and checkbox-ng) being already in the Debian and Ubuntu archives, we're working on getting proper i18n support ready.
I've posted a few initial patches
that add gettext_domain to provider definitions. With that we can add
additional APIs to expose the domain over DBus (or localized strings,
though I don't like that approach) and our python APIs.
PlainBox is just a framework for testing applications and we must deal with a lot of data to get everything right (only a fraction of the text on screen is actually in the program code). One of the biggest sources of data are test providers.
One of the challenges that we yet have to solve is how to tie this system with Launchpad's automatic translation system. For python code it's all okay but we need to ensure that launchpad is correctly exporting all the marked strings from our data files. If we manage to do that in time, translators can fill in the blanks and everyone using Ubuntu 14.04 will get new translations as a part of periodic language pack updates.