Samsung
Add an Alternate Calendar auf Samsung
Samsung's Calendar app defaults to the standard Gregorian calendar. Lunar and religious calendars like the Korean Lunar Calendar, Chinese Lunar Calendar, Vietnamese Lunar Calendar, Hijri, and Shamsi stay hidden until you activate them manually.
Once enabled, the app displays the extra date in smaller text underneath each day, without replacing your main calendar view. This is useful for tracking festivals, holidays, or family events tied to a different calendar system.
Where to turn it on
Open Calendar, then tap the Menu icon. From there go to Settings ➔ Alternate calendar and pick the calendar system you want to add.
Only one alternate calendar can be active at a time. Switching to a different one replaces the previous secondary dates instead of stacking multiple systems.
If the option doesn't appear in Settings, check whether Calendar app updates are pending, since older versions of Samsung's calendar sometimes hide this menu depending on your region settings.