There has been quite a few rumours saying that Forza Horizon 5 would take place in Japan. Some of them have been wishful thinking, and others comes from somewhat more reputable sources. But, according to two well known insiders, this is all wrong.
We're talking about Klobrille and the GamesBeat editor Jeff Grubb, who both say the Japan rumour is wrong. They also agree about another thing, and that is that we can expect it to be shown at E3 in June.
While this isn't an official confirmation, it's about as good sources as we're going to get when it comes to insiders, so we'd file all his under "Likely".