Where did anaconda crash for you? Are doing an install from boot.iso or something?
Just after language selection and just before time zone selection. If I selected English and Japanese, I got a crash in the module that creates the time zone map. If I selected English only it went fine. I was installing from a DVD that I burned from an .iso I got on the torrent, media check passed fine. I filed a bugzilla...
Is there any way to add Japanese support now?
The easiest thing is to look at comps.xml in the "Japanese Support" section where you're find a list of the packages that are usually installed for Japanese, and then install those: you probably don't need all of them but installing all shouldn't cause any problems.
I installed a package called kde-i18n-japanese which seems to have done the trick.