The "ZIP / Postal Code" found in common.php and/or js.php is untranslatable, despite being correctly wrapped in the __() function.
See screen grab from PO Edit here:
http://img571.imageshack.us/img571/346/skrmavbild20130605kl094.png
I have added updated line numbers and re-saved using the latest version of PO Edit (and updated the mo file). But this does not seem to work.