Reminds me of the message at the Peace Park in Hiroshima, which is translated on the stone in English as "Rest in peace, for the mistake will not be repeated."
The Japanese reads 「安らかに眠って下さい 過ちは 繰返しませぬから」
So one way might be just 「繰返しませぬ」 (Of course, this is the -ません form of 繰り返す, but rendered more poetically as ませぬ). However, this is problematic because there is an unnamed subject that must be doing the action--"We will not do it again," or "They will not do it again," or something like that.
I would guess something like 「再び起こりませぬ」 might also work and avoid the subject problem; I borrowed the use of ませぬ from the Peace Park example. But it also takes away the flavor of responsibility that 繰返しませぬ seems to have.
But I'm not really sure--just speculating.
The motto of the Jewish Defense League is "Never again", so that's another way you might be able to find an official translation.
The Japanese reads 「安らかに眠って下さい 過ちは 繰返しませぬから」
So one way might be just 「繰返しませぬ」 (Of course, this is the -ません form of 繰り返す, but rendered more poetically as ませぬ). However, this is problematic because there is an unnamed subject that must be doing the action--"We will not do it again," or "They will not do it again," or something like that.
I would guess something like 「再び起こりませぬ」 might also work and avoid the subject problem; I borrowed the use of ませぬ from the Peace Park example. But it also takes away the flavor of responsibility that 繰返しませぬ seems to have.
But I'm not really sure--just speculating.
The motto of the Jewish Defense League is "Never again", so that's another way you might be able to find an official translation.
Edited: 2011-05-12, 3:20 am

) and most of the sites that I was able to find either give a copy-paste of the Wikipedia entry with the untranslated motto, or don't mention the motto at all.