As far as I can see, this change allows the user to put a string name (like COM_FABRIK_LIST_NO_DATA_MSG) into the List Empty configuration field, and it will then be replaced with the local language string. 

If the field is blank, the above string is used anyway, but we get double translation. Would this not be better as:

return JText::_($params->get('empty_data_msg', 'COM_FABRIK_LIST_NO_DATA_MSG'));

??