AI is less likely to launch a nuclear strike when it reasons in Japanese

In more ways than one, yes.

It may depend on how genre-savvy the character is, in the story being emitted by the LLM. Perhaps the narrative demands that they attack the nuclear-empowered monster with a nuclear weapon because it's a necessary story-point to drive home the theme.

True. In the West, nuclear radiation creates super heroes, while in Japan, it produces devastating kaiju.

I wonder what accounts for the difference?