Open Radar

 
I'd like to generate localised string from the following code:
```
let skills = ["nunchuck", "bow hunting", "computer hacking"]
let notLocalizedJoined = skills.joined(separator: ", ")
```

Looking at the wikipedia article for "comma", not only is there different kinds of separators, but the elements are ordered differently or some languages mightn't have a separator at all.

And this is to say nothing about generating a list where optionally, say in English, the word "and" could precede the final element:
```
"nunchuck, bow hunting and computer hacking"
```

Turns out there's an `icu::ListFormatter` class in the ICU libraries, maybe it's time for an `NSListFormatter`?

I would have loved to submit a pull request implementing this in the Swift Foundation project but I quickly realised CoreFoundation should be consistent and offer the same functionality upon which the Swift Foundation project should bridge. If only CoreFoundation was open source *hint*!

https://en.m.wikipedia.org/wiki/Comma#In_other_languages
http://icu-project.org/apiref/icu4c/classicu_1_1ListFormatter.html
https://forums.swift.org/t/localised-string-array-join/10241