Dato is a replacement for the system menu bar clock. By default, it looks exactly the same, but when you click it, you get a small calendar, calendar events, the current time in various time zones, and more.
Dato supports all the locales and languages that macOS supports for the menu bar text, dates, times, and the calendar, but the menus are English-only.
The calendar and events are read-only. There’s currently no support for adding/editing events.
There are no plans to add support for the Chinese lunar calendar.