Ha, that's interesting food for thought. It never occurred to me that the "I will repay you" could be interpreted otherwise. Especially, as the German translation says "Ich werde Dich nicht enttäuschen", meaning "I won't disappoint you". So, no wonder, it never occurred to me to question my interpretation. Now it would be interesting to know whether the German translaters just followed their own interpretation of that scene or whether they discussed it with someone who wrote the original. I suppose they didn't.