You should not just translate Limesurvey in your local .po file, but participate in the community and add your translations here: translate.limesurvey.org
translate.limesurvey.org/projects/limesurvey-4/pt-br/default/
The Brazilian translation is lacking quite a bit. However, it is mostly marked as "fuzzy", very few translations are actually missing.
In any way, I searched for the two terms "To participate in this restricted survey, you need a valid token." and "If you have been issued a token, please enter it in the box below and click continue." and they don't seem to appear as strings to translate.
However, which version of Limesurvey are you using? Because I found a string that is called "If you have been issued an access code, please enter it in the box below and click 'Continue'." which would actually match the second one and then "To participate in this restricted survey, you need a valid access code.", which should be the first one.
So you notice that in the translation they are actually now talking about "access code" instead of "token". Now the question is, where the problem is. To me it seems like a bug where in the language file "token" has been changed to "access code", but the survey might still be using token.
I guess you "won" a bug report: bugs.limesurvey.org