Some time after updating from Mavericks to Yosemite, I noticed that the Vietnamese holidays were gone from the native Calendar app. They had appeared previously, I believe based on my regional settings. I went to Calendar help and followed these instructions to the "T" but with no effect: Show Holidays 1. In Calendar, choose Calendar>Preference. Then click General. 2. Select "Show Holidays calendar." To change your region (to display different holidays) choose Apple menu>System Preferences, click Language & Region, then choose your region. In Calendar preferences, deselect "Show Holidays calendar" and select it again. As I said, I followed this exactly but no Vietnamese holidays. If I switch my Region setting back to US and follow this procedure, the US holidays reappear even if I leave my timezone on Indochina time. There is a check box in Calendar>Preference>General which lets one shift to Chinese, Hebrew or Islamic. I don't want another whole calendar, just the Gregorian with Vietnamese holidays overlaid. Has anyone else had this or a similar experience involving any other country?