Future-proof .po files will be hard to come by until we get a stable release, and we're still several releases away from that. Keeping them up to date has to be the responsibility of the Ãœbercart community because none of know anything besides English. (I may do an Esperanto translation at some point, if I get enough of a vocabulary and free time.) We're going to update the .pot files with each release to make the translation job easier, and any changes will hopefully be easy to find.