iOS has independent settings for language [prefered languages], and another for date format/currency/etc [region settings].
If I am understanding it right, you want to be able to change the date format [region settings] only on your app? Different from the [region setting] that is choosen on settings?
PS: Can´t the user just set their prefered date format on region settings globally while keeping freedon on chosing another language? (I know this is not what you are asking here, but I'm curious about why the user would need a different region format just for some apps. (you dont'd need to answer me my curiosity, I am just expressing myself)
Please just confirm my first question [if I am correctly understanding what you need] so I can try to help you.
Thanks! In Settings you can enable 24-hour time or change the region or calendar, which changes the date format, but they may not want to change those globally. They may want another language/region's date formatting options in my app. iOS 13 allows the user to specify a language for each individual app but this app only supports English localizations (minus the date customizations).