Well, they do use Nostradamus' prophecies as a basis for the date of 1999 and it may seem plausible that they used it for the location of Japan as well:
"The year 1999, seventh month,
From the sky will come a great King of Terror:
To bring back to life the great King of the Mongols,
Before and after Mars to reign by good luck."
(Century 10, Quatrain LXXII)
Three quatrains later:
"Long awaited he will never return
In Europe, he will appear in Asia:
One of the league issued from the great Hermes,
And he will grow over all the Kings of the East."
(Century 10, Quatrain LXXV)
It was an interesting change, no doubt, and I have no clue if any actual writings influenced it or not, but it was quite a pleasant surprise to see this while reading over the 1999 verse.