Tolkien actually penned two responses to the query, saying to his publisher, "Personally I should be inclined to refuse to give any Bestätigung [confirmation] (although it happens that I can), and let a German translation go hang. In any case I should object strongly to any such declaration appearing in print... You are primarily concerned, and I cannot jeopardize the chance of a German publication without your approval. So I submit two drafts of possible answers."
I believe the other response was a simple acknowledgement that ignored the question, and that which of the two was actually sent is not known.