I heard this claim before but I also read Shigeru Mizuki's autobiographical manga and it depicts his father listening to the radio and he says something to the effect of "I think the war is over".

I don't know if Mizuki's father would be more inclined to understand the message, whether he understood classical Japanese or not.

For that matter, did the Emperor of Japan speak in a classical dialect distinct from the general population?

Edit: To be clear this would be World War II.