Okay, not sure why but those don’t get translated. I have the standard WordPress fields like First name. Last Name, Password all hard coded in on line 245 in the user-reg-aide-options.php file. It calls those from an array on the front end so that may be why they do not translate. Anyways, what I am thinking is just change the display names or second part of the array key after the => and in between the “” to the desired name in your language. Sort of hard for me to work with since I have no translation files so I had to install a spanish version of WordPress on my test machine.
To make a long story short, in my spanish version, I changed the display name in that known fields array starting on line 345 in the user-reg-aide-options.php file after the => in between the “” and it worked fine, all I had to do was change the selected fields for the front end. As for your own custom fields you can also change the field title on the edit new fields page.
Hope that helps