Localization in SwiftUI

This week I want to talk about another crucial feature of any app, which is Localization. Every user expects that your app correctly uses environment features like the right-to-left layout or uses system locale to format dates or currencies. Another vital thing here is translations, and this week, we will learn which tools SwiftUI provides to add in our apps as many languages as we can.

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LocalizedStringKey is a special struct which is provided by the SwiftUI framework. It conforms ExpressibleByStringLiteral protocol, which allows us to create this struct by using a String value. Text component, on the other hand, has an overload that accepts LocalizedStringKey instead of String. It allows us to use our localization keys in a very transparent way. Let’s take a look at a quick example.

let goal: LocalizedStringKey = "goal"
let text = Text(goal)

LocalizedStringKey looks for a “goal” key in translation files, and as soon as it finds provided translation for a key “goal” it will replace the key with a correct translated string. In the case where there is no provided translation, it will use the key as a dummy string value.

To learn how to create translation files, take a look at the “Internationalization and Localization” guide provided by Apple.

String interpolation

We already know how to localize static text in our apps. But what about the dynamic text, where we need to inject some data like names or some numeric values. Fortunately, LocalizedStringKey conforms ExpressibleByStringInterpolation protocol, which allows us to use String interpolation to pass data into our string values. Let’s take a look at a small example.

let name = "Majid"
Text("myNameIs \(name)")

In the example above, we create a Text component with the “myNameIs (name)” string value. As you already know, the Text component has an init method overload, which accepts LocalizedStringKey and LocalizedStringKey conforms ExpressibleByStringInterpolation, and this is all the magic behind the localization in SwiftUI. This piece of code will look for the “myNameIs %@” key in your translation files. Let’s take a look at how our translation file should look to make it work.

"myNameIs %@" = "My name is %@.";

I have to mention that it doesn’t work in preview canvas. You should run it on simulator.

String interpolation is a compelling feature of Swift language. By using String interpolation, we can also pass stuff like formatters or format specifiers, which can provide additional presentation logic. Let’s take a look at a few code examples.

let date = Date()
let formatter = DateFormatter()
formatter.dateStyle = .medium
formatter.timeStyle = .none
Text("birthday \(date, formatter: formatter)")

In the code sample above, we pass a DateFormatter, which converts a Date representation into a proper localized string value. This code will run a localized string lookup and then apply the formatter. Here is how the translation file should look.

"birthday %@" = "My birthday is %@.";

Let’s take a look at another quick sample where we inject integer into our translation.

let age = 28
Text("age \(age)")

"age %lld" = "I'm %lld years old";


Localization is an essential aspect in the world of user experience. Today we learned how easily we could localize our apps with the help of LocalizedStringKey struct provided by SwiftUI. I hope you enjoy the post. Feel free to follow me on Twitter and ask your questions related to this post. Thanks for reading, and see you next week!