Hey Lucas, We use the standard joomla strings and that is why you are not finding them in our language file. If your joomla is in portuguese-BR, then it should automatically translate these strings.
look at utils.php
$_PN_LT = JText::_('<');
$_PN_RT = JText::_('>');
$_PN_START = JText::_( 'Begin' );
$_PN_PREVIOUS = JText::_( 'Prev' );
$_PN_NEXT = JText::_( 'Next' );
$_PN_END = JText::_( 'End' );
Open your joomla translation and find 'prev' next and so on. If those strings are not existing, then add them to the file and then it should work.