If you set $wgBookManagerv2JsonEditor to true and try editing a Book namespace page, <bookmanagerv2-publication-date-field-field> shows up as the label for the date field.
There is a message named 'bookmanagerv2-publication-date-field' so this might be a bug in the message key generation?
Version: unspecified
Severity: normal
Change 120362 had a related patch set uploaded by Deepali:
Remove edit toolbar from the editing form
Change 120362 had a related patch set uploaded by Deepali:
Fix label for publication date in json editor
Declining because BookManagerv2 is an archived extension now. Please see T178938: Archive the BookManagerv2 extension for details. All Gerrit patches were already abandoned long ago.