Ios localization

Skill almasumdev/awesome-ios-agent-skills/.github/skills/ui/ios-localization

Curated agent skills, conventions, and workflows for building iOS apps (Swift, SwiftUI, UIKit) with AI coding agents.

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npx -y skills add almasumdev/awesome-ios-agent-skills --skill ios-localization

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Expert guidance on iOS localization — String Catalogs (.xcstrings), ICU plurals and genders, right-to-left layout, and dynamic locale switching. Use when adding or auditing translated content.

SKILL.md

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iOS Localization & Internationalization

Instructions

Use String Catalogs (.xcstrings, Xcode 15+). They replace Localizable.strings + .stringsdict, support ICU plurals natively, and sync keys automatically.

1. String Catalog Basics

File → New → File → String Catalog. Name it Localizable.xcstrings.
Any String(localized:) or Text(_:) literal is extracted on build.
Add locales from the catalog's inspector; Xcode fills keys on build.

Text("article.save.button")                 // Key-based
Text("Save")                                // String-based (auto-extracted)
String(localized: "greeting.hello", defaultValue: "Hello, World")

Prefer semantic keys ("article.title.placeholder") over raw English for anything that might be rephrased.

2. Interpolation

let name = "Sam"
Text("greeting.user \(name)")
// Catalog entry: "greeting.user %@" → "Hello, %@!"

For numbers and dates, use format specifiers or FormatStyle:

Text("\(count, format: .number)")
Text("\(date, format: .dateTime.day().month().year())")
Text("\(amount, format: .currency(code: "USD"))")

3. Plurals (ICU)

String Catalogs expose a Vary by Plural option directly in the editor. Under the hood:

Text("inbox.unread \(count)")
// "one"   -> "1 unread message"
// "other" -> "%lld unread messages"

For older codebases, a .stringsdict with the NSStringLocalizedFormatKey still works.

4. Gender and Width Variants

String Catalogs support device variants (iPhone/iPad/Mac/watch) and width classes. Use them for titles that need shorter forms on compact layouts:

profile.title
  default: "Your Profile"
  compact: "Profile"

5. Right-to-Left (RTL)

SwiftUI mirrors automatically when the locale is RTL. Write layouts with leading/trailing, never left/right:

HStack { Image(systemName: "chevron.backward"); Text("Back") }
    .padding(.leading, 16)

Force a preview:

#Preview("Arabic") {
    RootView()
        .environment(\.locale, .init(identifier: "ar"))
        .environment(\.layoutDirection, .rightToLeft)
}

Use .flipsForRightToLeftLayoutDirection(true) on custom drawings (e.g., arrows) that must mirror.

6. Dynamic Locale Switching

The OS drives the locale, but apps can override per-scene:

struct RootView: View {
    @AppStorage("preferredLanguage") private var lang: String = ""

    var body: some View {
        ContentView()
            .environment(\.locale, lang.isEmpty ? .autoupdatingCurrent : Locale(identifier: lang))
    }
}

To persist beyond the current scene, set UserDefaults "AppleLanguages" (requires restart to fully apply across all frameworks).

7. Formatting Rules

Never concatenate translated strings — always interpolate.
Never assume word order; give translators full sentences.
Always provide context via the comment: parameter:

String(localized: "cart.checkout.cta",
       defaultValue: "Check out",
       comment: "Button title on the cart screen confirming purchase.")

8. Testing

Run with Double-Length Pseudolanguage and Right-to-Left Pseudolanguage to surface layout bugs.
Snapshot tests in every locale you ship — see the ios-testing skill.
Lint for hardcoded strings using SwiftLint rule strict_fileprivate and custom rules.

Checklist

All user-visible strings come from String(localized:) / Text.
String Catalog is the single source of truth; no loose .strings files for new modules.
Plurals use catalog variants, never string concatenation.
Layouts use leading/trailing; custom drawings mirror for RTL.
Every key has a translator-facing comment:.
Pseudolanguage tests pass.