Thank you for the reply. I spent a bit more time on it before coming back to the forum and came up with a solution. Something I should have known is that you need to install the Japanese language on English Windows for anything to work. This is likely the cause of the blank error message, no characters to display. Then After Effects would launch anyway and revert back to default English(?).
What worked for me under Windows 10 (English):
1. Uninstall After Effects
2. Go to Windows Settings > Time & Language > Region & Language

3. Install the language you want ('+ Add a language')
4. Click on the language and 'Set as default'
5. Reboot (Windows will boot in the new language)
6. Install After Effects again
I was able to install After Effects CC2017 in English and CC2015 in Japanese using this method. You can switch back and forth by setting one or the other as default and rebooting.
Thanks again for the reply, Szalam.
I don't know if your solution would have worked but I'll keep that in mind for the future. It's definitely something to try before hitting the forums.
Mike