The Calendar app on the iPhone and iPad supports alternate calendars, including Chinese, Hebrew, and Islamic. By default, in America, it's set to U.S. format. However, you can easily change it to any of the other formats. Here's how!
How to enable Chinese, Hebrew, or Islamic formats in Calendar for iPhone or iPad
Launch the Settings app on your iPhone or iPad.
Tap on Mail, Contacts, Calendars.
Tap on Alternate Calendars under the Calendars section.
Tap on any one of the supported alternate calendars you'd like to use instead of the standard format.
Your Calendar app should now reflect those changes.