This issue blocks T215039.
As @thiemowmde noted at https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/Wikibase/+/491057/2/repo/i18n/en.json@128:
there is at least one place in SpecialMergeLexemes that uses this message with Message::escape(), which would output this wikitext as escaped plain text. This place (and possibly more, please check) needs to be updated before this message can be updated.