The most reasonable explanation is that this is developed by (an) Apple user(s) and adding support for Apple's languages is simply easier and more valuable than

The most reasonable explanation is that this is developed by (an) Apple user(s) and adding support for Apple's languages is simply easier and more valuable than adding languages for a platform they don't use. If it's worth it to you or other C# users, I'm sure they wouldn't mind you submitting a pull request.