Progress % of a Language & Language constants

Hi, I have installed the Romanian language pack which has a Progress of 70%.
I have contacted the author to see if they can work on it more but i wanted to ask, how is the % calculated.

Also, how do i add more language constants as many sections are in ruins especially the Edit Profile section. See example attached example, everything is in Romanian apart from that last bit that says 'Your password is case sensitive'.

I can see the language override and i was able to look for constants but it only brings up the ones that have been translated already. Is there a way of bring up a list of the rest?

Thanks for your reply.