How to change calendar settings on my iPhone?

Re: How to change calendar settings on my iPhone? : I want change calendar language and add calendar region

Seems you can change language and region overall for the iPhone

How to: Change the language and region on iPhone - Apple Support

and

You can choose to display the Chinese, Hebrew, or Islamic calendar etc (alongside the Gregorian calendar)

Change calendar and event settings on iPhone - Apple Support

or

if needed: Schedule or display events in a different time zone in Calendar on iPhone - Apple Support

or

This (non-Apple) wikiHow shows you how to change the regional settings for your iPhone's calendar.

https://www.wikihow.com/Change-the-Calendar-Region-on-an-iPhone