Adding Thousand Separator to Int in Swift

You can use NSNumberFormatter to specify a different grouping separator as follow:

update: Xcode 11.5 • Swift 5.2

extension Formatter {
    static let withSeparator: NumberFormatter = {
        let formatter = NumberFormatter()
        formatter.numberStyle = .decimal
        formatter.groupingSeparator = " "
        return formatter
    }()
}

extension Numeric {
    var formattedWithSeparator: String { Formatter.withSeparator.string(for: self) ?? "" }
}

2358000.formattedWithSeparator  // "2 358 000"
2358000.99.formattedWithSeparator  // "2 358 000.99"

let int = 2358000
let intFormatted = int.formattedWithSeparator  // "2 358 000"

let decimal: Decimal = 2358000
let decimalFormatted = decimal.formattedWithSeparator  // "2 358 000"

let decimalWithFractionalDigits: Decimal = 2358000.99
let decimalWithFractionalDigitsFormatted = decimalWithFractionalDigits.formattedWithSeparator // "2 358 000.99"

If you need to display your value as currency with current locale or with a fixed locale:

extension Formatter {
    static let number = NumberFormatter()
}
extension Locale {
    static let englishUS: Locale = .init(identifier: "en_US")
    static let frenchFR: Locale = .init(identifier: "fr_FR")
    static let portugueseBR: Locale = .init(identifier: "pt_BR")
    // ... and so on
}
extension Numeric {
    func formatted(with groupingSeparator: String? = nil, style: NumberFormatter.Style, locale: Locale = .current) -> String {
        Formatter.number.locale = locale
        Formatter.number.numberStyle = style
        if let groupingSeparator = groupingSeparator {
            Formatter.number.groupingSeparator = groupingSeparator
        }
        return Formatter.number.string(for: self) ?? ""
    }
    // Localized
    var currency:   String { formatted(style: .currency) }
    // Fixed locales
    var currencyUS: String { formatted(style: .currency, locale: .englishUS) }
    var currencyFR: String { formatted(style: .currency, locale: .frenchFR) }
    var currencyBR: String { formatted(style: .currency, locale: .portugueseBR) }
    // ... and so on
    var calculator: String { formatted(groupingSeparator: " ", style: .decimal) }
}

Usage:

1234.99.currency    // "$1,234.99"

1234.99.currencyUS  // "$1,234.99"
1234.99.currencyFR  // "1 234,99 €"
1234.99.currencyBR  // "R$ 1.234,99"

1234.99.calculator  // "1 234.99"

Note: If you would like to have a space with the same width of a period you can use "\u{2008}"

unicode spaces

formatter.groupingSeparator = "\u{2008}"