Hi.
I tried to find similar thread and downloaded this file.

Downloading BlackBerry Handheld Software v4.6.1.428 (EastAsia)

8520wifijEastAsia_PBr4.6.1_rel428_PL4.2.0.124_A4.6 .1.290_Rogers_Wireless_Inc.exe

And install this exe file.
Install finished successfully and opened my Blackberry Desktop Manager
to install Japanese symble.

With Application loader, I tried to add and delate application, and also tried to renew the sofeware but there is nothing I can upgrade to use Japanese.

Please let me know how should I do next.
Thank you!

If you mean Japanese text entry, to my knowledge, such functionality is not available, except if you buy a Bold 9000 from NTT DoCoMo in Japan. And before you ask, no, the DoCoMo Bold 9000 OS cannot be installed in your 8520.

For the 8520, Japanese text display should work out of the box. If it doesn't you don't need to reinstall the OS, just simply add the Japanese language option.