⚠️ Security fixes

• JSON locale data for invalid locales is no longer cached on disk; instead a 404 error is triggered. This avoids creating small files in the cache folder for each invalid locale that is requested. (#4766)

🎏 Internationalization

• New translation: Ukrainian 🇺🇦

🎉 Improvements

• Add a new "Until approved" option for a registration form's "Modification allowed" setting (#4740, thanks @vasantvohra)
• Show last login time in dashboard (#4735, thanks @vasantvohra)
• Allow Markdown in the "Message for complete registrations" option of a registration form (#4741)
• Improve video conference linking dropdown for contributions/sessions (hide unscheduled, show start time) (#4753)
• Show timetable filter button in conferences with a meeting-like timetable

🐛 Bugfixes

• Fix error when converting malformed HTML links to LaTeX
• Hide inactive contribution/abstract fields in submit/edit forms (#4755)
• Fix adding registrants to a session ACL

🔧 Internal Changes

• Videoconference plugins may now display a custom message for the prompt when deleting a videoconference room (#4733)
• Videoconference plugins may now override the behavior when cloning an event with attached videoconference rooms (#4732)