/ios-localization

String Catalogs (.xcstrings) -- Detailed Reference

Contents

• What is a String Catalog?
• Creating a String Catalog
• Automatic String Extraction
• Manual Key Management
• Handling Strings in Non-SwiftUI Code
• Bundle Access Patterns
• Multi-Module / SPM Localization
• Pluralization in String Catalogs
• Device Variations
• Exporting for Translators (XLIFF / xcloc)
• String Catalog JSON Structure
• Generated Localizable Symbols (Xcode 26+)
• Testing Strategies
• Migration from .strings / .stringsdict
• Best Practices

What is a String Catalog?

A String Catalog is a single Xcode-managed .xcstrings file (JSON-based) that holds localizable strings in a target, along with translations, plural forms, and device variations. In Xcode 15 and later, String Catalogs are the recommended workflow for new localization work because they replace much of the manual synchronization previously required across .strings and .stringsdict files.

Availability: Xcode 15+, all Apple platforms. String Catalogs are the recommended Xcode 15+ workflow for app localization. Xcode 26 adds generated localizable symbols on top of String Catalogs; do not describe catalogs themselves as requiring Xcode 26 or iOS 17.

Creating a String Catalog

1. File > New > File > String Catalog
2. Name it Localizable.xcstrings (the default table name, matching the legacy Localizable.strings)
3. Place it in the target's source directory
4. Add target languages in Project > Info > Localizations

For a non-default table name (e.g., Onboarding.xcstrings), reference it explicitly:

String(localized: "welcome.title", table: "Onboarding")

Automatic String Extraction

On every build, Xcode scans source files and extracts strings from known localizable initializers. Extraction is compiler-driven -- it recognizes these patterns:

SwiftUI (LocalizedStringKey)

Text("Hello, world")                        // extracted
Label("Settings", systemImage: "gear")      // extracted
Button("Save") { }                          // extracted
Toggle("Enable notifications", isOn: $on)   // extracted
.navigationTitle("Home")                     // extracted
Section("Account") { }                      // extracted

// NOT extracted -- computed or variable strings
Text(viewModel.title)                       // not extracted (runtime value)
Text(verbatim: "v1.2.3")                    // not extracted (verbatim skips localization)

Foundation (String(localized:))

String(localized: "No results found")               // extracted
String(localized: "error.title",
       defaultValue: "Something went wrong",
       comment: "Generic error alert title")         // extracted with default + comment

LocalizedStringResource

LocalizedStringResource("Order placed")              // extracted
static var title: LocalizedStringResource = "Title"  // extracted

What is NOT extracted

let x: String = "Not localized"          // plain String assignment
print("debug info")                      // not user-facing
NSLocalizedString("legacy", comment: "") // legacy API; Xcode can export literal keys

Prefer String(localized:), SwiftUI localizable literals, or LocalizedStringResource in new Swift code so String Catalog syncing and generated-symbol workflows stay straightforward. If automatic extraction misses a string, add it manually in the String Catalog editor.

Manual Key Management

Open the .xcstrings file in Xcode to use the visual editor:

• Add key: Click + at the bottom of the key list
• Remove key: Select key, press Delete (marks as Stale, removed on next build if no code reference)
• Edit comment: Select key, edit the Comment field (provides translator context)
• Mark state: Right-click a translation to set Needs Review / Reviewed
• Vary by plural: Select a key, click Vary > Plural to add plural categories
• Vary by device: Select a key, click Vary > Device to add iPhone/iPad/Mac variants

Key naming conventions

For manually-managed strings, use stable symbol-style keys rather than English text as the key. This prevents silent localization breaks when UI copy changes (a typo or rewording just creates a new key and stales the old one — no compiler error). With Xcode 26's generated symbols, stable keys also produce readable, predictable Swift accessors.

onboarding.welcome.title        -> "Welcome"
onboarding.welcome.subtitle     -> "Get started in minutes"
settings.notifications.toggle   -> "Enable Notifications"
error.network.title             -> "Connection Error"
error.network.message           -> "Check your internet and try again"

Use String(localized:defaultValue:) when you want a structured key that differs from the English text:

let title = String(localized: "error.network.title",
                   defaultValue: "Connection Error",
                   comment: "Title for network error alert")

For SwiftUI auto-extracted strings, the literal text IS the key by default. This is fine for simple views. For any string you manage manually — shared keys, keys referenced across modules, or keys where copy changes frequently — use a stable key instead.

Handling Strings in Non-SwiftUI Code

View models, services, and utilities

class OrderService {
    func statusMessage(for order: Order) -> String {
        switch order.status {
        case .shipped:
            return String(localized: "order.status.shipped",
                          defaultValue: "Your order has shipped!",
                          comment: "Order status when item is in transit")
        case .delivered:
            return String(localized: "order.status.delivered",
                          defaultValue: "Delivered on \(order.deliveryDate!, format: .dateTime.month().day())",
                          comment: "Order status with delivery date")
        case .processing:
            return String(localized: "order.status.processing",
                          defaultValue: "Processing your order...",
                          comment: "Order status while being prepared")
        }
    }
}

Specifying table and bundle

// From a specific table
String(localized: "greeting",
       table: "Onboarding",
       comment: "First-launch greeting")

// From a specific bundle (framework or Swift package)
String(localized: "button.save",
       table: "SharedUI",
       bundle: .module,
       comment: "Save button in shared component")

Bundle Access Patterns

Main app

// Uses Bundle.main by default -- no bundle argument needed
String(localized: "Hello")

Swift Package (SPM)

// .module refers to the package's resource bundle
String(localized: "Hello", bundle: .module)

// In SwiftUI, pass the package bundle explicitly for package resources
Text("Hello", bundle: .module)

Framework

// Reference the framework's bundle
let frameworkBundle = Bundle(for: MyFrameworkClass.self)
String(localized: "Hello",
       bundle: .init(frameworkBundle.bundleURL))

Multi-Module / SPM Localization

Each Swift package target that contains user-facing strings needs its own String Catalog.

Package.swift setup

let package = Package(
    name: "SharedUI",
    defaultLocalization: "en",
    targets: [
        .target(
            name: "SharedUI",
            dependencies: [],
            resources: [
                .process("Resources")  // Localizable.xcstrings goes here
            ]
        )
    ]
)

Directory structure

Sources/
  SharedUI/
    Resources/
      Localizable.xcstrings    <- String Catalog for this module
    Views/
      ButtonStyles.swift

Accessing strings from the package

// Inside the package -- bundle: .module resolves package-owned resources
public struct SaveButton: View {
    public var body: some View {
        Button(String(localized: "Save", bundle: .module)) { }
    }
}

Important: Code outside the main app bundle needs an explicit bundle. Use bundle: .module in Swift packages, Bundle(for:) in frameworks, or the current-target bundle macro when available.

For Swift package localization failures, answer with this explicit resource checklist before bundle debugging:

1. Package.swift declares defaultLocalization.
2. The target resources list processes the catalog location, such as .process("Resources").
3. Localizable.xcstrings is actually inside that processed target-resource path. Only after those pass, debug lookup with bundle: .module or Text(..., bundle: .module).

Pluralization in String Catalogs

Setup

1. Write code with integer interpolation:

   Text("\(itemCount) items in your cart")

2. Build the project -- Xcode adds the key to the String Catalog
3. Open the String Catalog, select the key
4. Click "Vary by Plural" in the inspector
5. Fill in plural forms for each language

English plural forms

one:   "%1$(itemCount)lld item in your cart"
other: "%1$(itemCount)lld items in your cart"

Arabic plural forms (all six categories)

zero:  "لا توجد عناصر في سلتك"
one:   "عنصر واحد في سلتك"
two:   "عنصران في سلتك"
few:   "%lld عناصر في سلتك"        (3-10)
many:  "%lld عنصرًا في سلتك"       (11-99)
other: "%lld عنصر في سلتك"         (100+)

Multiple plural variables

When a string has two integer interpolations, the String Catalog shows a matrix of plural combinations:

Text("\(photoCount) photos in \(albumCount) albums")
// English needs: one/one, one/other, other/one, other/other

Device Variations

Enable "Vary by Device" for a key to provide different text on iPhone, iPad, Apple Watch, Mac, Apple TV, and Apple Vision Pro.

// Code is the same everywhere:
Text("Tap to continue")

// String Catalog provides:
// iPhone: "Tap to continue"
// iPad:   "Tap or click to continue"
// Mac:    "Click to continue"
// Vision: "Look and tap to continue"

Exporting for Translators (XLIFF / xcloc)

Export

1. Product > Export Localizations... (or xcodebuild -exportLocalizations)
2. Select target languages
3. Xcode creates .xcloc bundles (one per language)
4. Send .xcloc files to translators (they contain XLIFF 1.2 inside)

Command-line export

xcodebuild -exportLocalizations \
    -project MyApp.xcodeproj \
    -localizationPath ./Localizations \
    -exportLanguage de -exportLanguage ja -exportLanguage ar

Import

1. Product > Import Localizations...
2. Select the completed .xcloc file
3. Xcode merges translations into the String Catalog
4. Review changes in the diff viewer

Command-line import

xcodebuild -importLocalizations \
    -project MyApp.xcodeproj \
    -localizationPath ./Localizations/de.xcloc

String Catalog JSON Structure

The .xcstrings file is Xcode-managed JSON. Understanding the observed structure can help with parser-backed validation or careful batch updates, but prefer Xcode's editor/export/import workflows for normal localization changes and validate any automated edit before committing.

{
  "sourceLanguage": "en",
  "version": "1.0",
  "strings": {
    "Welcome, %@!": {
      "comment": "Greeting shown on home screen with user name",
      "localizations": {
        "en": {
          "stringUnit": {
            "state": "translated",
            "value": "Welcome, %@!"
          }
        },
        "de": {
          "stringUnit": {
            "state": "translated",
            "value": "Willkommen, %@!"
          }
        }
      }
    },
    "room_available": {
      "comment": "Button label on room search results",
      "extractionState": "manual",
      "localizations": {
        "en": {
          "stringUnit": {
            "state": "translated",
            "value": "Book this room"
          }
        }
      }
    },
    "%1$(count)lld items": {
      "localizations": {
        "en": {
          "variations": {
            "plural": {
              "one": {
                "stringUnit": {
                  "state": "translated",
                  "value": "%1$(count)lld item"
                }
              },
              "other": {
                "stringUnit": {
                  "state": "translated",
                  "value": "%1$(count)lld items"
                }
              }
            }
          }
        }
      }
    }
  }
}

Note the "room_available" key above: it uses "extractionState": "manual" and a stable symbol-style key with the English text in "value", not in the key itself. Use stable manual keys for generated-symbol strings. Avoid source-copy-derived keys for API-facing strings because wording edits can rename generated identifiers and churn call sites.

Translation states

• "new" -- Xcode extracted the key but no translation exists
• "translated" -- Translation provided
• "needs_review" -- Marked for review (source string changed or manual flag)
• "stale" -- Key no longer found in code (removed on next clean build)

Extraction states

The extractionState field (separate from translation state) tracks how a key entered the catalog:

The manual state is significant: manual keys have the Generate Swift Symbol checkbox enabled by default, so they automatically produce compiler-checked LocalizedStringResource accessors when the build setting is on. Auto-extracted keys can also generate symbols — enable the checkbox per-key or use Refactor > Convert Strings to Symbols.

Generated Localizable Symbols (Xcode 26+)

Generated symbols are an Xcode 26 typed-access layer on top of String Catalogs; do not describe catalogs themselves as requiring Xcode 26 or iOS 17.

Enabling symbol generation

1. Build Settings > Localization > Generate String Catalog Symbols → Yes (on by default in new Xcode 26 projects)
2. The catalog must use format version "1.1" — Xcode 26 writes this automatically when symbol generation metadata is present
3. Each key has a Generate Swift Symbol checkbox in the String Catalog editor. Manual keys (added via the (+) button) have this enabled by default. Auto-extracted keys can opt in via Refactor > Convert Strings to Symbols, which enables the checkbox

How Xcode derives symbol names

Xcode camelCases the key name, lowercasing the first segment:

Keys with format specifiers become functions. Use positional named placeholders such as %1$(name)lld for descriptive argument labels; bare %lld produces generic labels:

You can rename parameters during refactoring for more descriptive signatures.

Using generated symbols

// Simple key — static property
Text(.roomAvailable)

// Parameterized key — function
Text(.landmarksCount(count: 42))

// Non-default table (Booking.xcstrings)
Text(.Booking.confirmBookingCta)

// In non-SwiftUI code
let title = String(localized: .roomAvailable)
let attributed = AttributedString(localized: .greeting(userName))

Code completion supports generated symbols — type . and choose from the menu.

Refactoring existing strings to symbols

Select one or more keys in the String Catalog editor, Control-click, and choose Refactor > Convert Strings to Symbols. Xcode replaces string literal usage in code with the generated symbol. This is reversible via Convert Symbols to Strings.

Cross-module limitations

Generated symbols are declared internal. Code in other modules cannot access them directly. Default to a public wrapper; reach for xcstrings-tool if the wrapper becomes unwieldy across many modules:

• Public wrapper (default): Create a public extension on LocalizedStringResource that delegates to the internal symbols
• xcstrings-tool: A Swift Package Plugin that generates public constants from .xcstrings files — use this for heavier multi-module setups where maintaining manual wrappers becomes tedious

For Swift Packages, the generated symbols use the .module bundle automatically. The internal visibility means only code within the same package target can reference them.

Testing Strategies

Scheme language override

Edit Scheme > Run > Options > App Language. Choose any added language to launch the app in that locale without changing the device/simulator system language.

Pseudolocalization options

Xcode provides built-in pseudolocalization modes (Edit Scheme > Run > Options > App Language):

UI tests with locale override

func testGermanLayout() {
    let app = XCUIApplication()
    app.launchArguments += ["-AppleLanguages", "(de)"]
    app.launchArguments += ["-AppleLocale", "de_DE"]
    app.launch()

    // Verify no truncation on key screens
    let saveButton = app.buttons["Speichern"]
    XCTAssertTrue(saveButton.exists)
    XCTAssertTrue(saveButton.isHittable)
}

Snapshot testing per locale

Use a snapshot testing library to capture screenshots in multiple locales and compare them for layout regressions:

let locales = ["en_US", "de_DE", "ar_SA", "ja_JP"]
for locale in locales {
    app.launchArguments = ["-AppleLanguages", "(\(locale.prefix(2)))"]
    app.launch()
    // Capture and compare snapshot
}

Translation coverage validation

Check that all keys are translated before release:

# Parse the .xcstrings JSON and check for "new" or empty states
python3 -c "
import json, sys
with open('Localizable.xcstrings') as f:
    data = json.load(f)
missing = []
for key, info in data['strings'].items():
    for lang, loc in info.get('localizations', {}).items():
        unit = loc.get('stringUnit', {})
        if unit.get('state') in ('new', None) or not unit.get('value'):
            missing.append(f'{lang}: {key}')
if missing:
    print('Missing translations:')
    for m in missing: print(f'  {m}')
    sys.exit(1)
print('All translations complete.')
"

Migration from .strings / .stringsdict

Automatic migration

1. Select the .strings file in the project navigator
2. Right-click > Migrate to String Catalog...
3. Xcode creates a .xcstrings file with all existing keys and translations
4. Verify in the String Catalog editor
5. Remove the old .strings / .stringsdict files from the target

Manual migration

If automatic migration fails (complex bundle setups, CocoaPods):

1. Create a new Localizable.xcstrings
2. Build to extract keys from code
3. Copy translations from old .strings files into the String Catalog editor
4. Copy plural rules from .stringsdict into plural variants
5. Remove old files

Migration checklist

• All .strings keys present in the new String Catalog
• All .stringsdict plural rules converted to String Catalog plural variants
• Bundle references updated (if custom bundle was used)
• Build succeeds with no missing-localization warnings
• Test every language the app supports
• Remove old .strings and .stringsdict files from the target
• Commit the .xcstrings file (it is JSON, diffs well in version control)

Coexistence

String Catalogs and .strings files can coexist in the same target during migration. Xcode resolves keys from the String Catalog first, then falls back to .strings. Remove legacy files after verifying the migration.

Best Practices

1. One String Catalog per target -- keep Localizable.xcstrings as the single source of truth for each target.
2. Use comments -- provide context for every ambiguous key. Translators cannot see your UI.
3. Review extraction on every build -- new keys appear with state "new". Translate them promptly.
4. Version control the .xcstrings file -- it is JSON and diffs clearly. Review translation changes in PRs.
5. Automate coverage checks -- integrate translation-coverage validation in CI to catch missing translations before release.
6. Export regularly -- send updated .xcloc bundles to translators after each sprint or feature merge.
7. Test with pseudolocalizations in CI -- run UI tests with double-length and RTL pseudo-languages to catch layout issues early.
8. Prefer stable keys with generated symbols -- for manually-managed strings, use symbol-style keys and enable Generate String Catalog Symbols to get compile-time safety and autocompletion.