swift-i18n

Development

Automatic internationalization for Swift/SwiftUI apps. Use when writing ANY user-facing text - always localize with String Catalogs, LocalizedStringResource, and proper pluralization patterns.

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Swift Internationalization (i18n)

MANDATORY: All User-Facing Text Must Be Localized

Every string displayed to users MUST use localization APIs. Never hardcode strings.

Modern APIs (Swift 5.7+)

String(localized:) - Swift Code

// Basic usage with comment for translators
let title = String(
    localized: "home.welcome.title",
    defaultValue: "Welcome",
    comment: "Main screen welcome title"
)

// In Swift Packages - ALWAYS specify bundle
let text = String(localized: "feature.title", bundle: .module)

LocalizedStringResource - Type-Safe (Swift 5.9+)

extension LocalizedStringResource {
    enum App {
        enum Home {
            static let title = LocalizedStringResource(
                "app.home.title",
                defaultValue: "Home",
                comment: "Navigation title for home screen"
            )
            static func itemCount(_ count: Int) -> LocalizedStringResource {
                LocalizedStringResource(
                    "app.home.itemCount",
                    defaultValue: "\(count) items",
                    comment: "Item count with pluralization"
                )
            }
        }
    }
}

// Usage
Text(LocalizedStringResource.App.Home.title)

SwiftUI Text - Automatic Localization

// Literal strings ARE localized automatically
Text("home.title")
Button("button.save") { }

// String variables are NOT localized - wrap them!
let key = "home.title"
Text(LocalizedStringKey(key)) // Required for variables

Pluralization

// Number in text triggers plural rules
Text("You have \(count) items")
// xcstrings: "You have %lld items" with plural variations

Date/Number Formatting

Text(date, style: .date)
Text(price, format: .currency(code: "EUR"))
Text(count, format: .number)

Key Naming Convention

module.screen.element.property

Examples:

app.home.title
auth.login.button.submit
profile.settings.toggle.notifications

Anti-Patterns

// NEVER DO THIS
Text("Welcome")              // Hardcoded
let msg = "Hello \(name)"    // String interpolation outside Text
Text(msg)                    // Variable not localized

// ALWAYS DO THIS
Text("welcome.message")
Text("greeting.hello \(name)")
Text(LocalizedStringKey(dynamicKey))

Preview Multi-Locale Testing

#Preview("English") {
    ContentView()
        .environment(\.locale, Locale(identifier: "en"))
}

#Preview("French") {
    ContentView()
        .environment(\.locale, Locale(identifier: "fr"))
}