I don't know if we'll have an automatic language switch depending
on browser settings.
A compromise might be to emphasize the mechanism for switching
language if the user's browser is set to another language than the
current. This way, if a japanese user comes to the site he'll more
easily see that it is actually available in japanese, but his
default will still be english.
I am not sure why you do not want to show the site in japanese when
the user has requested japanese by default...
Experiment: set your browser preferred language to French, Swedish,
whatever. Go to www.google.com. What do you see?
JMarc