If you’re a detail-oriented iOS developer, one of the things you’ve probably had drilled into you is that you should alwys localise user facing strings. Thankfully in Cocoa we have a variety of tools at our disposal to do this, from simple .strings files, to the .stringsdict file format: which lets us handle more specialised strings with pluralisation rules.

That said, it can make your code look messy to have dozens of calls to NSLocalizedString() all over the place, and this only gets more out of control when using NSString.localizedStringWithFormat(_:, comment:) to handle format strings.

Thankfully, there’s a Swifty solution we can employ to make our code read just a bit more clearly: type extensions. By extending the String type, we can turn these long, messy lines of code:

self.navigationItem.title = NSLocalizedString("Notes", "Navigation title for the notes screen")
self.notesCountLabel.text = NSString.localizedStringWithFormat(NSLocalizedString("%lu Notes", comment: "The number of notes"), self.viewModel.notesCount)

Into something that looks like this:

self.navigationItem.title = .notesNavigationTitle
self.notesCountLabel.text = .notesCount(self.viewModel.notesCount)

The magic that makes these lines of code work is a simple extenison to the String type, which we can stick at the bottom of a view controller’s file, or put in its own swift file called something like String+Localized.swift to make it available throughout our codebase.

extension String {
    // A regular localised string in a `.strings` file
    static let notesNavigationTitle = NSLocalizedString("Notes", "Navigation title for the notes screen")

    // A localised format string with pluralization rules declared in a `.stringsdict` file
    func notesCount(_ count: Int) -> String {
      NSString.localizedStringWithFormat(NSLocalizedString("%lu Notes", comment: "The number of notes"), count)
    }
}

You can take this approach even further with a tool like SwiftGen, which can take your Localizable.strings file and generate type-safe Swift code from it, but on a smaller project, the approach above can really make your code easier to read.