Union Workshop have moved on to TSW, so there's no commercial developer left to do japanese content. (Chinese routes were made by SimtechVision, but they were all pretty low quality efforts.) Though I've seen some impressive screenshots from a freeware project on rail-sim.de, not sure if it's abandoned though.
That is no fun to find out. Seems that TSC is dying as many have moved to TSW which I find no interest in. I love these Japanese routes on TSC and have hoped for more.
Looks like a nice run but sadly there has never been that strong a following to make Japanese content, as noted above only UW. If it's JR East there's an outside chance Ongakukan could do it for their video clip based sim, but I found those to be a bit unsatisfactory as it really just feels like driving the video clip.
