Localize IOS

Localize Swift

Localize UIKit Views and ViewControllers and SwiftUI Views: extract hardcoded strings, generate consistent keys, replace literals with the correct Swift API, and create or update the .xcstrings String Catalog.

Overview

String Catalogs (.xcstrings, Xcode 15+) are the Apple-recommended localization format. This skill guides extraction of hardcoded strings, generation of camelCase keys, and replacement with typed APIs (String(localized:) or xcstrings-tool's .localizable(...)).

Rules

See rules index for detailed patterns covering:

• Always use String Catalogs over legacy .strings files
• LocalizedStringKey vs. String(localized:) API selection
• Plural rules and string interpolation patterns
• Accessibility label localization
• RTL layout considerations
• Testing localized content

Workflow

1. Check xcstrings-tool

This step is a hard gate. Do not read the target file, extract strings, propose keys, or take any other action until this step reaches a terminal outcome. The workflow does not advance until one of the two outcomes below is confirmed.

Search for xcstrings-tool in Package.swift and for XCStringsToolPlugin in project.pbxproj.

Outcome A — Already installed: note it and move to step 2.

Outcome B — Not installed: inform the user it is not present, explain the benefit (compile-time key safety), and ask: "Would you like to install xcstrings-tool before continuing, or proceed without it?" Then stop and wait.

• If the user says no / skip: note that String(localized:) will be used throughout, then move to step 2.
• If the user says yes: follow the installation steps in references/xcstrings-tool.md → Installation, ask them to build (Cmd+B), then verify XCStringsToolPlugin appears in project.pbxproj. If not found, inform the user the plugin is still missing and do not advance. Only move to step 2 once confirmed present.

2. Read the target file

Read the Swift file the user points to. Classify it as one of:

• View layer — UIKit ViewController, UIView subclass, SwiftUI View
• ViewModel / Presenter — class or struct that owns display-intent properties (e.g. title, message, buttonLabel) consumed by a view
• Helper / Formatter / Enum — produces strings that eventually reach the UI (e.g. an enum with a var title: String switch, a date formatter returning display text)

The classification affects the replacement API (see step 6) but all three types can contain strings that need localization.

3. Extract hardcoded strings

Find all raw string literals that represent user-visible text. For ViewModel and helper files, apply the data-flow heuristic in references/key-naming.md → User-Facing Strings in ViewModels and Helper Classes to determine whether each string reaches the UI. See the full exclusion list there as well.

Present all candidates to the user before making changes.

4. Propose localization keys

Use camelCase — featureNameComponentNameDescription. Derive the prefix from the file name or feature folder.

See references/key-naming.md for naming rules and conflict resolution. Present the full key list to the user and confirm before making any changes. Accept corrections.

5. Update the .xcstrings file

See references/xcstrings-format.md for exact JSON structure.

1. Search the project for all *.xcstrings files.

   • If more than one is found, ask the user which file to add the new keys to before proceeding.
   • If exactly one is found, use it directly.
   • If none is found, create one (see step 2).

2. Creating Localizable.xcstrings — locate the Resources folder in the main target. Identify it by the presence of any of: *.xcassets directories, .mp4 files, .json files, or other static resource files. Inside Resources, create a Localization/ subfolder and write Localizable.xcstrings there using the base structure from references/xcstrings-format.md:

   Resources/
   └── Localization/
       └── Localizable.xcstrings
   

   Then immediately register it in project.pbxproj by running the bundled script:

   swift sh .claude/skills/localize-ios/scripts/add_to_xcodeproj.swift \
     "path/to/App.xcodeproj" \
     "path/to/Resources/Localization/Localizable.xcstrings" \
     --group Localization
   

   The script will:

   • Detect the main app target automatically (by productType = "com.apple.product-type.application")
   • Create a Localization PBXGroup if it doesn't exist, nested under the parent Resources group
   • Add the file reference with path = Localizable.xcstrings (the group's path handles the directory)
   • Add the build file to the correct target's PBXResourcesBuildPhase

   Verify the script output confirms the target name, file reference UUID, and build file UUID.

   Unless the user explicitly requests otherwise, the .xcstrings file must always belong to the main app target. Use --target "TargetName" to override if needed.

3. Add each new key as an entry under "strings" with:

   • "extractionState": "manual"
   • A "comment" describing context for translators
   • The source string as the English value with "state": "new"

4. Check for existing translations. Search project.pbxproj for the knownRegions array to detect all languages configured in the project. Do not rely on inspecting the .xcstrings file itself. For each language code found in knownRegions other than en and Base:

   • Add a "localizations" entry for that language on every new key
   • Provide the actual translation — do not copy the English value
   • Set "state": "translated"
   • If you are not confident in the translation accuracy, set "state": "needs_review" and add a note in the report

6. Replace strings in the Swift file

Apply API selection in this order:

1. xcstrings-tool installed → use typed API (.localizable(...)) everywhere in the target.
2. xcstrings-tool not installed → use String(localized:).
3. Cross-target exception: file belongs to a target without XCStringsToolPlugin → use String(localized:, table:).

See references/xcstrings-tool.md → Usage by Context for code patterns covering UIKit, SwiftUI, and switch statements.

7. Report results

After all changes, output:

• A table of replaced strings → keys
• Path to the created/updated .xcstrings file
• xcstrings-tool recommendation if not installed
• Next steps: add translations in Xcode's String Catalog editor, then build to regenerate typed accessors

Examples

Positive Trigger

User: "Localize ProfileViewController.swift"

Expected behavior: Read the file, extract all hardcoded user-facing strings, propose camelCase keys, confirm with the user, replace strings with String(localized:), and create/update Localizable.xcstrings.

Non-Trigger

User: "Fix the layout bug in ProfileViewController where the button is clipped."

Expected behavior: Do not use this skill. Investigate and fix the layout issue directly without invoking the localization workflow.

Troubleshooting

Switch statement strings not replaced

• Error: Raw string literals inside switch cases remain hardcoded after running the workflow.
• Cause: Each switch case returns a String and must be wrapped individually — there is no single call site.
• Solution: Replace each case's string literal with String(localized: "key") or .localizable(.key) one by one.

.xcstrings file not found

• Error: No Localizable.xcstrings file exists in the project.
• Cause: The project has not been localized yet.
• Solution: Create Resources/Localization/Localizable.xcstrings using the base structure from references/xcstrings-format.md, then run scripts/add_to_xcodeproj.swift (via swift sh) to register it in project.pbxproj. Both steps are required — the file must exist on disk AND be referenced in the project.

.xcstrings file created but missing in Xcode

• Error: Localizable.xcstrings exists on disk but does not appear in Xcode's project navigator and is not bundled.
• Cause: The file was written to disk but project.pbxproj was not updated.
• Solution: Run scripts/add_to_xcodeproj.swift (via swift sh) with the correct .xcodeproj path and file path. Confirm the script output shows the target and group where the file was added, then reopen the project in Xcode.

xcstrings-tool typed accessors missing after adding keys

• Error: After adding keys to .xcstrings, .localizable(...) properties are not available.
• Cause: xcstrings-tool runs as a build-time plugin — it regenerates Swift types only when the project builds.
• Solution: Build the project (Cmd+B in Xcode) to trigger code generation. If the types still do not appear, verify the plugin is added to the app target's Build Phases.

.xcstrings file added to wrong target

• Error: Localizable.xcstrings is registered in project.pbxproj but xcstrings-tool does not generate typed accessors, or the strings are not found at runtime.
• Cause: The file was added to an extension target's PBXResourcesBuildPhase instead of the main app target's.
• Solution: The add_to_xcodeproj.swift script automatically finds the main app target by productType = .application. If you need a specific target, use --target "TargetName". For manual fixes, move the build file entry from the extension target's PBXResourcesBuildPhase to the main app target's phase.

Localizable.xcstrings registered under wrong group in Xcode navigator

• Error: Xcode build error "The file 'Localizable.xcstrings' couldn't be opened because there is no such file" even though the file exists on disk.
• Cause: scripts/add_to_xcodeproj.swift created the Localization PBXGroup but nested it under the wrong parent group (e.g. UI instead of Resources). Xcode resolves the file path by walking the group chain, so the wrong parent causes the resolved path to differ from the actual disk path.
• Solution: Verify in project.pbxproj that the Localization group appears in the children array of the Resources group (not any other group). If it is under the wrong parent, remove the entry from the wrong group's children array and add it to the Resources group's children array.

Key naming conflict with existing entries

• Error: A proposed key already exists in .xcstrings with a different source string.
• Cause: The same key was reused across different UI contexts.
• Solution: Make the key more specific by adding more context segments, e.g. featureConfirmButtonLabel instead of featureLabel.