Per consensus, please install the Quiz extension on the Japanese Wikibooks.
I'll try to do it myself.
Change 714873 had a related patch set uploaded (by 4nn1l2; author: 4nn1l2):
[operations/mediawiki-config@master] Install Extension Quiz on ja.wikibooks
Scheduled to be deployed during morning backport window on 26 August.
Change 714873 merged by jenkins-bot:
Mentioned in SAL (#wikimedia-operations) [2021-08-26T18:19:26Z] <urbanecm@deploy1002> Synchronized wmf-config/InitialiseSettings.php: 66717bc039f40336144dcc0dfd97ff5331b418e9: Install Extension Quiz on ja.wikibooks (T289383) (duration: 01m 05s)