A simple protocol to enable a collection of Pluralizable objects to return either the singular or the plural, depending on the count of the collection.

Puralizable.swift

protocol Pluralizable {
    static var singular: String { get }
    // Override with the correct plural, if simply appending an "s" is incorrect
    static var plural: String { get }
}

extension Pluralizable {
    static var singular: String {
        return String(describing: self)
    }

    static var plural: String {
        return "\(singular)s"
    }
}

extension Collection where Element: Pluralizable {
    var pluralize: String {
        return count == 1 ? Element.singular : Element.plural
    }

    var pluralizeCount: String {
        return "\(count) \(pluralize)"
    }
}

z_PluralizableUsage.swift

struct Capital {}
extension Capital: Pluralizable {}

[Capital]().pluralize // "Capitals"
[Capital()].pluralize // "Capital"
[Capital(), Capital()].pluralize // ""Capitals


struct Country {}

extension Country: Pluralizable {
    static var plural: String {
        return "Countries"
    }
}

[Country]().pluralizeCount // "0 Countries"
[Country()].pluralizeCount // "1 Country"
[Country(), Country()].pluralizeCount // "2 Countries"