I want to create an iphone app with localized text and images for a variety of languages/cultures. Is there a native way to do this in Unity or do I need to create a custom .NET library that reads XML files?
You can use Application.systemLanguage to get the user's OS language - but any higher level localization you need to do yourself.
Since a google search on "localization unity" didn't turn up anything relating to native support, I think you will have to do something on your own.
Didn't look much at it, but this also looks cool http://forum.unity3d.com/threads/35617-TextManager-Localization-Script
I have made an asset for localization using Excel. Please take a look and let me know what you think !
If you’re involved in software localization projects, you might want to check out this great, collaborative online localization tool: https://poeditor.com/