How to get OS language and locale?

My app changes the language at runtime and advises the user to restart the app. I do it like this:

    typealias LanguageLocaleType = (language: String?, locale: String?, title: String)

    let elements: [LanguageLocaleType] = [
        (nil, nil, "System Default"),
        ("en", "en_US", "English"),
        ("ar", "ar_SA", "Arabic"),
    ]

    //...func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath)...

    let element = elements[indexPath.row]

    guard let language = element.language else {
        // How to really reset app back to OS language/locale???
        UserDefaults.standard.removeObject(forKey: "AppleLanguages")
        UserDefaults.standard.removeObject(forKey: "AppleLocale")
        return
    }

    UserDefaults.standard.set([language], forKey: "AppleLanguages")

    if let locale = element.locale, !locale.isEmpty,
        Locale.current.identifier != locale,
        !Locale.current.identifier.hasPrefix("\(language)_") {
            UserDefaults.standard.set(locale, forKey: "AppleLocale")
    }

I want to offer to set languages in a list with the right one selected, one of which being offered it to set language back to System Default. However, there's no way to find the OS-level language and locale that I could find. Since after I mess around with setting the UserDefaults, Bundle.main.preferredLocalizations is not reliable and do not match the system default (event when I remove the key from the User Default).

Is there a way to get the OS-level language and locale instead of the app-level?