flutter-slang-i18n

name: flutter-slang-i18n description: Add and maintain Slang localization in Flutter projects. Use when Codex needs to introduce slang, slang_flutter, or slang_build_runner, migrate hardcoded Flutter UI strings into Slang translations, scan Dart code for user-visible strings, or review existing Slang keys for semantic fit.

Flutter Slang I18n

Workflow

1. Check project state before edits.

   • Run git status --short and follow the repository's change-safety policy before modifying files.
   • Find the Flutter package root containing pubspec.yaml.
   • If .fvm/fvm_config.json exists, run Flutter and Dart commands through fvm.
   • Inspect existing localization (slang.yaml, build.yaml, lib/i18n, intl, ARB, easy_localization) before adding another system. If replacing an existing i18n stack, call out migration risk first.

2. Add Slang using current package names.

   • Prefer the official packages slang, slang_flutter, and, when using build_runner, slang_build_runner plus build_runner.
   • If a request mentions flutter_slang, verify the package name before using it; Slang's Flutter support package is normally slang_flutter.
   • Use the project command style:

     fvm flutter pub add slang slang_flutter
     fvm flutter pub add flutter_localizations --sdk=flutter
     fvm flutter pub add -d build_runner slang_build_runner
     

     Drop fvm only when the project is not using FVM.
   • Add a base translation file such as lib/i18n/en.i18n.json and a peer locale such as lib/i18n/zh-CN.i18n.json when the product supports Chinese.
   • Use slang.yaml for fvm dart run slang; use build.yaml for build_runner integration. Keep the generated output path consistent with the existing project style.
   • When creating a new Slang config, set translate_var: S instead of Slang's default t:

     translate_var: S
     

     For build_runner, put the same option under targets.$default.builders.slang_build_runner.options.
   • If an existing project already uses the generated t variable, changing translate_var to S is a breaking source change. Tell the user explicitly, then update every t.<key> call site or keep the existing variable name if the user does not want that break.
   • Generate code with fvm dart run slang or fvm dart run build_runner build -d, matching the chosen setup.

3. Wire Flutter integration.

   • Import the generated file, usually package:<app>/i18n/translations.g.dart.
   • Initialize locale handling in main, for example LocaleSettings.useDeviceLocale().
   • Wrap the app with TranslationProvider when using Slang locale handling.
   • Set MaterialApp.locale, supportedLocales, and localizationsDelegates so Flutter framework strings also localize.
   • In widgets that must rebuild on locale changes, prefer final S = Translations.of(context) or the project's context extension style.

4. Scan hardcoded strings, then confirm by context.

   • Run scripts/scan_dart_strings.py from this skill against the target Flutter project:

     uv run python /path/to/flutter-slang-i18n/scripts/scan_dart_strings.py --root /path/to/flutter/project
     

     If the target environment does not use uv, run the executable script directly.
   • Treat scanner output as candidates, not truth. Review surrounding code before changing anything.
   • Localize user-visible UI strings: Text, labels, hints, tooltips, dialogs, snackbars, validation messages, empty states, errors shown to users, semantics labels, and accessibility copy.
   • Usually skip non-UI strings: imports, asset paths, route paths, analytics event names, log/debug messages, test fixtures, protocol values, enum names, storage keys, and Key or ValueKey values.

5. Replace strings with semantic Slang keys.

   • Add keys that describe product/UI intent, not only the current English words.
   • Preserve interpolation and formatting with Slang parameters, pluralization, and contexts when applicable.
   • Keep shared keys only for identical meaning across contexts. Do not reuse a key just because two English strings currently match.
   • Update all locale files together. If a translation is unknown, add a clear placeholder consistent with the repo's localization policy and flag it in the final response.

6. Audit existing Slang usage.

   • Find generated translation use:

     rg -n "\b(context\.)?[tS]\.|Translations\.of\(context\)" lib
     

   • Compare each key path with the surrounding UI. Rename keys like title, text1, ok, or stale copied feature names when they no longer describe the UI intent.
   • Key renames break source references and translation files. State this explicitly, update every call site and locale, and avoid hidden compatibility aliases unless the user agrees.
   • Read references/slang-review-guidelines.md for key naming and triage rules when the audit is non-trivial.

7. Validate.

   • Run code generation after translation changes.
   • Run fvm dart run slang analyze when Slang CLI is configured, and fix missing or unused translations relevant to the change.
   • Run fvm dart format on changed Dart files.
   • Run the narrowest useful checks: generated i18n compile test, widget tests around changed screens, or fvm flutter test when the change spans shared UI.
   • Report scan limitations and any strings intentionally left hardcoded.

Resources

• scripts/scan_dart_strings.py: Regex/lexer-based Dart scanner for likely hardcoded UI strings.
• references/slang-review-guidelines.md: Triage rules for hardcoded strings and semantic Slang key review.