iOS – and Apple OSs in general – have excellent I18N support. You more or less don’t have to worry about date and number formatting as long as you are following the rules. The essential rules are:
- all translations are prepared beforehand and compiled into the app
- language choice is done outside your app, in system' Settings
Fairly often, I have requests from clients to implement in-app language change, which should (at least) instantly translate the app. There is no API support in iOS frameworks for this.
It’s not impossible though.