All his translations (but a few early ones) are based off the English translations, approved by Mishima.

One of Mishima's pet obsessions was how much was lost/twisted in translation. He was incomfortable with the whole idea of translation he thought a betrayal, and greatly mistrusted translations from the Japanese he believed wasn't understood well enough by western translators, and as he couldn't judge himself of the results... English was the sole western language he could read more or less fluently, so eventually he announced these approved/revised English translations would be considered his original for westerners, and all further western translations had to be done from them.

Some scholars don't agree with Mishima that the English translation are all that great and put his reading skills of English into question (some local specialist of Japanese litterature wrote an article on this years ago, pointing with examples how much he thought Mishima's prose had lost from the translation from English instead of a direct Japanese to French translation, especially now that there are really excellent French-Japanese translators), so I guess one day (once he gets into the public domain, probably) new translations from the original Japanese will surface, a bit like has happened with the new French translations of Dostoievsky (but not with results as "dramatic" as that - or as Kundera's early novels, I'd expect).