Installation:
- extract KoboRoot.tgz from the uploaded archive
- copy it to .kobo of your device, safely eject and disconnect
- after the device has rebooted, select Japanese as user language (Settings > Language > 日本語)
This will survive FW updates.
Note: This works only for English. For other languages you would have to apply the suggestions in post #1 (but of course extract the qm file of your language, or create a qm file of your language yourself, cf.
this thread).
Uninstall:
Use uninstall_qms.zip which is uploaded to
this post.