Localized lists in Swift

LocalizeLists.swift

extension SequenceType where Generator.Element == String {
    func localizedJoin() -> String {
        var g = self.generate()
        guard let first = g.next() else {
            return ""
        }
        guard let second = g.next() else {
            return first
        }
        guard var last = g.next() else {
            return String.localizedStringWithFormat(NSLocalizedString("%@ and %@", comment: "List; only two items"), first, second)
        }
        var middle = second
        while let piece = g.next() {
            middle = String.localizedStringWithFormat(NSLocalizedString("%@, %@", comment: "List; more than three items, middle items"), middle, last)
            last = piece
        }
        return String.localizedStringWithFormat(
            NSLocalizedString("%@, and %@", comment: "List; more than two items, last items"),
            String.localizedStringWithFormat(NSLocalizedString("%@, %@", comment: "List; more than two items, first items"), first, middle),
            last)
    }
}