In many places in your applications, you create String instances dynamically or display string literals to the user. To display translated versions of these strings, you must create a strings table. A strings table is a file containing a list of key-value pairs for all of the strings that your application uses and their associated translations. It is a resource file that you add to your application, but you do not need to do a lot of work to get data from it.

You might use a string in your code like this:

let greeting = "Hello!"

To internationalize the string in your code, you replace literal strings with the function NSLocalizedString(_:comment:).

let greeting = NSLocalizedString("Hello!", comment: "The greeting for the user")

This function takes two arguments: a key and a comment that describes the string’s use. The key is the lookup value in a strings table. At runtime, NSLocalizedString(_:comment:) will look through the strings tables bundled with your application for a table that matches the user’s language settings. Then, in that table, the function gets the translated string that matches the key.

Now you are going to internationalize the strings that the MapViewController displays in its segmented control. In MapViewController.swift, locate the loadView() method and update the initializer for the segmented control to use localized strings.

override func loadView() {
    // Create a map view
    mapView = MKMapView()

    // Set it as *the* view of this view controller
    view = mapView

    let segmentedControl
            = UISegmentedControl(items: ["Standard", "Satellite", "Hybrid"])

    let standardString = NSLocalizedString("Standard", comment: "Standard map view")
    let satelliteString
            = NSLocalizedString("Satellite", comment: "Satellite map view")
    let hybridString = NSLocalizedString("Hybrid", comment: "Hybrid map view")
    let segmentedControl
          = UISegmentedControl(items: [standardString, satelliteString, hybridString])

Once you have files that have been internationalized with the NSLocalizedString(_:comment:) function, you can generate strings tables with a command-line application.

Open the Terminal app. This is a Unix terminal; it is used to run command-line tools. You want to navigate to the location of MapViewController.swift. If you have never used the Terminal app before, here is a handy trick. In Terminal, type the following:

cd

followed by a space. (Do not press Return yet.)

Next, open Finder and locate MapViewController.swift and the folder that contains it. Drag the icon of that folder onto the Terminal window. Terminal will fill out the path for you. It will look something like this:

cd /Users/cbkeur/iOSDevelopment/WorldTrotter/WorldTrotter/

Press Return. The current working directory of Terminal is now this directory.

Use the terminal command ls to print out the contents of the working directory and confirm that MapViewController.swift is in that list.

To generate the strings table, enter the following into Terminal and press Return:

genstrings MapViewController.swift

The resulting file, Localizable.strings, contains the strings from MapViewController. Drag this new file from Finder into the project navigator (or use the File → Add Files to "WorldTrotter"... menu item). When the application is compiled, this resource will be copied into the main bundle.

Open Localizable.strings. The file should look something like this:

/* Hybrid map view */
"Hybrid" = "Hybrid";

/* Satellite map view */
"Satellite" = "Satellite";

/* Standard map view */
"Standard" = "Standard";

Notice that the comment above your string is the second argument you supplied to the NSLocalizedString function. Even though the function does not require the comment argument, including it will make your localizing life easier.

Now that you have created Localizable.strings, you need to localize it in Xcode. Open its file inspector and click the Localize... button in the utility area. Make sure Base is selected from the pop-up and click Localize. Add the Spanish and English localization by checking the box next to each language.

In the project navigator, click on the disclosure triangle that now appears next to Localizable.strings. Open the Spanish version. The string on the lefthand side is the key that is passed to the NSLocalizedString(_:comment:) function, and the string on the righthand side is what is returned. Change the text on the righthand side to the Spanish translations shown below. (To type an accented character, such as “é,” press and hold the appropriate character on your keyboard and then press the appropriate number from the pop-up.)

/* Hybrid map view */
"Hybrid" = "Hybrid" "Híbrido";

/* Satellite map view */
"Satellite" = "Satellite" "Satélite";

/* Standard map view */
"Standard" = "Standard" "Estándar";

Build and run the application again. Now all these strings, including the titles in the segmented control, will appear in Spanish (Figure 7.18). If they do not, you might need to delete the application, clean your project, and rebuild. (Or check your scheme language setting.)

Figure 7.18  Spanish MapViewController

Internationalization and localization are very important for your app to reach the largest audience. Additionally, as you saw early in this chapter, your app might not work for some users if you have not properly internationalized it. You will internationalize (but not localize) your projects in the rest of this book.

Over the past five chapters, you have built a rather impressive application that allows the user to convert between Celsius and Fahrenheit as well as display a map in a few different ways. Not only does this application scale well on all iPhone screen sizes, but it is also localized into another language. Congratulations!