Swift 4 update for https://medium.com/@dcordero/a-different-way-to-deal-with-localized-strings-in-swift-3ea0da4cd143

Localizer.swift

import Foundation

private class Localizer {
    
    static let sharedInstance = Localizer()
    
    lazy var localizableDictionary: NSDictionary! = {
        if let path = Bundle.main.path(forResource: "Localizable", ofType: "plist") {
            return NSDictionary(contentsOfFile: path)
        }
        
        fatalError("Localizable file NOT found")
    }()
    
    func localize(string: String) -> String {
        
        guard let localizedValue = localizableDictionary[string] as? NSDictionary else {
            assertionFailure("Missing translation for: \(string)")
            return ""
        }
        
        guard let localizedString = localizedValue["value"] as? String else {
            assertionFailure("Missing translation for: \(string)")
            return ""
        }
        
        return localizedString
    }
}

extension String {
    var localized: String {
        return Localizer.sharedInstance.localize(string: self)
    }
}