[Ghoulish Delight]

Perhaps he just doesn't like/isn't good at translating the other way. I know that even when I was still close to fluent in Spanish, it would have been easier for me to translate something from Spanish into English than vice versa. Or it may be that he just doesn't want to do it for his own work. I found this quote from him:

"Sometimes a book appeals to me because I want to introduce it to Japanese readers. That's one reason. Another reason is that I want to learn something from this book, and translation is the best way. You can read every detail, every page, every word. You can learn so much. It's my teacher. I want to try many different styles. Translation is a kind of vehicle. One time you can write F. Scott Fitzgerald and one time Raymond Chandler. It's a transformation."

Seems to indicate the latter reason.