At https://github.com/wikimedia/mediawiki-extensions-CentralNotice/blob/a5b313996b23484e29b9a6cd2a1cdbf091803214/includes/Banner.php#L1551 we can find the config that adds the protection reason displayed on CentralNotice.
We should make that a translatable message in the /i18n folder for CentralNotice, and said message to be output in the wiki content language (NOT user language) where CentralNotice actions are triggered.
Thanks.