If you know english (and I think you do), with a good dictionary in your hands each translation is easy. You can translate what you understand, therefore the point is another: bad expressed italian sentences are bad translated, and that's only up to the bad italian used, just like in this case (who the hell wrote it?!).
What does "una royalty pari al 4% sul fatturato a valore di produzione a [ditta X]" mean?
It may mean:
"una royalty pari al 4% del fatturato al valore di produzione per la ditta X",
but it could also mean:
"una royalty pari al 4% aggiunta al fatturato come valore di produzione per la ditta X",
as it could also mean a lot of other things, I think.
One much probable solution could be: "Plus a commission equal to 4% of the sales proceeds as production value for the company X."