Translation is a big part of Messenger Plus! Live and enables it to be used by the widest range of users possible.
Please read the following thread on the guidlines for translation
Translation guidelines for Messenger Plus! Live
There may be an existing translation in your regional version of portuguese (as I understand that Portuguese Portuguese and Brazilian Portuguese are different)
please look here
for a list of posts in threads in the translation forum containing the word 'portuguese' and you may find an existing project to help with and bring up to date for the version 4.79 beta