Why not 'très célèbre' vs. 'très connu' ?
"Célèbre" is accepted as well when you enter your own translation.
Is there a reason "en Japon" is not acceptable?
The reason is that "le Japon" is a masculine country: au Japon.
I tried to copy and paste the entire line because I'm sure that there's nothing else that could be a mistake. But copy and paste seems to have been disabled for my pixel 3. Reported April 2020.