Invite to repetitive appointment shows "Failed to read 'weeklyNthOnNounclass3' from chrome://calendar/locale/calendar-event-dialog.properties."

[tharrrk]

Received an invitation, I see the message "Failed to read 'weeklyNthOnNounclass3' from chrome://calendar/locale/calendar-event-dialog.properties."

It seems the functionality is not affected.

Console shows:
Failed to read 'weeklyNthOnNounclass3' from chrome://calendar/locale/calendar-event-dialog.properties.
Error: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIStringBundle.formatStringFromName]"
nsresult: "0x80004005 (NS_ERROR_FAILURE)"
location: "JS frame :: resource://calendar/modules/calUtils.jsm -> file:///home/tharrrk/.thunderbird/8n2zcjji.default/extensions/%7Be2fda1a4-762b-4020-b5ad-a41df1933103%7D/calendar-js/calUtils.js :: calGetString :: line 699" data: no]

Type: hosted on outlook.office365.com

Versions:
EWS: V2017_04_14 (15.1.1261.13)
XPI: 4.0.0-beta4
Lightning: 5.4
TB: 52.1.1 (64-bit)
OS: KDE neon User Edition 5.10 (based on Ubuntu Xenial 16.04) x86_64