You forgot that we agreed that interest rate is 0%, so you would have to return the same 1000$ (not 950$ as you pretend). But you can only earn 970$. In this case you incur a loss of 30$.
REAL interest rate of 0% implies NOMINAL interest rate of -5%.
If you borrow money at 0%, you will have to return the same amount that you borrowed (deflation, inflation, or whatever). I don't know what else is here to discuss. If you disagree, then you disagree, I have no more inclination to discuss this issue any further.
Actually, I don't already understand what you mean by real interest and what you mean by nominal interest.