I don't think there is a Brazilian translation (portuguese) available yet. It would be great if you could do this! . Please have a look at the TikiWikiInternationalizationAndLanguages page for more information on how exactly to create a new language.
If you have anymore questions, ask any of the people of the Translation Team or Sylvie Greverend (UserPagesylvie) who is in charge of the I18N efforts.