Bibtex using the wrong language!

Find plain.bst on your file system, copy the file, rename the file to something else. Open the file, add a comment that the name has changed and the current year and preferrably your name.

Find the edition function and replace it with the following block:

FUNCTION {format.edition}
{ edition empty$
    { "" }
    { output.state mid.sentence =
        { edition "l" change.case$ " Edi\c{c}\~ao" * }
        { edition "t" change.case$ " Edi\c{c}\~ao" * }
      if$
    }
  if$
}

Save your file. Put it in the same folder as your tex document (for now).

Change your document to use the new modified bibliographystyle.

Done.


Or use biblatex, it picks up the language used in the doument.


You can use babplain for a babel-aware version of plain part of the babelbib package see texdoc babelbib for more details.

You also need to add

\usepackage{babelbib}

so that it defines all the new fixed texts in an appropriate language.