You need to copy the FFXI install information from POL EU registry to the JPN POL registry.
Once you do that it will find the game and load it properly.
For whatever that matters all people playing FFXI have the exact same data besides a couple of data files which are unique *per install*.
well, here's a walkthrough that should work for everyone:
1-go to this page:
http://www.playonline.com/ff11/download/media/vista01.html?pageID=media
Download it by clicking "同意する" (agree to the EULA).
Install it, while having the system locale already set for Japan (it works with different locales but you will have problem typing Japanese ingame if the locale isn't Japan: aka it doesn't work at all)
2- After it's installed, let it update and then log your account in it.
3- Close it and perform these actions:
Copy registry key (including the hexadecimal number it contains) "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnlineUS\Interface\0001" or "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnlineEU\Interface\0001" to "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnline\Interface\0001"
Copy the whole "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnlineUS\SquareEnix\FinalFantasyXI" or "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnlineEU\SquareEnix\FinalFantasyXI" as "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnlineUS\SQUARE\FinalFantasyXI" key, as is.
Copy "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnlineUS\Interface\0001" or "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnlineUS\Interface\0001" as "HKEY_LOCAL_MACHINE\SOFTWARE\PlayOnline\Interface.
Both keys marked "0001" are used to identify the FFXI install and should be the exact same on all POL installs. It's possible to have all three versions of the POL Viewer client installed on the computer and they will operate properly without interfering with each other as long you perform this correctly.
Also I don't have plugins so I don't know if this has any effect on third party stuffs.
I just did all that stuff I posted above and ended with the pictured working install of the Japanese software.