Silverlight v4 Beta released for JPN
Silverlight v4 Beta JPN SDK is released at https://www.microsoft.com/downloads/details.aspx?displaylang=ja&FamilyID=a53019b2-4370-4e8a-a940-518f538c759f
Silverlight v4 Beta JPN SLtools is released at https://www.microsoft.com/downloads/details.aspx?displaylang=ja&FamilyID=68a158af-9bb8-4855-a724-d09d196eaaf3
If you have Dev10 Beta2 JPN installed, you can install JPN SLTools which will install developer runtime, JPN SDK and tools as part of the setup and you can create JPN Silverlight 4 apps.