This is indeed related to ONIX_BookProduct_CodeLists.xsd, which is maintained by the EDItEUR
folks. I asked them about translations back in April 2013 and they said that while at best only partial translations had been exchanged so far, and not with concerted management, they would be putting some effort into it this year. If you like, I can put you in touch with their folks to discuss progress and Portuguese in particular.
Public Knowledge Project Team