Romanized: Hiroshima to Nagasaki no daisanji ga mô nido to okorimasen yô ni Literally: (I pray) that the terrible events of Hiroshima and Nagasaki will never occur twice
Very sorry for reacting your message tooo late...
I think it is too late to answer but i would like to respond.
I think Ziken will not be suitable for this context...Sanji(惨事) or Dai-sanji(大惨事) is more suitable.
For japanese people,ziken sounds like case,for example,murder,robbery,assalt in bank...etc.
We,japanese do not consider Hiroshima and Nagasaki incident as Ziken,because incidents happend in war is more serious than any other cases.
If someone japanese see this translation in shrine,everybody do not understand 広島・長崎ã®äº‹ä»¶ is 広島・長崎ã®å¤§æƒ¨äº‹ at a glance.
I am japanese,so i feel this translation must be corrected.