Internationalization (i18n)

CheckAI supports 8 languages out of the box with full coverage of all user-facing strings in both the backend and the web frontend.

Supported Languages

Code	Language
en	English (default)
de	German
fr	French
es	Spanish
zh-CN	Chinese (Simplified)
ja	Japanese
pt	Portuguese
ru	Russian

Backend (Rust)

The backend uses the rust-i18n crate with YAML locale files.

Locale Files

Translations are stored in locales/*.yml:

locales/
├── en.yml
├── de.yml
├── fr.yml
├── es.yml
├── zh-CN.yml
├── ja.yml
├── pt.yml
└── ru.yml

Usage in Code

use rust_i18n::t;

// Simple key lookup
let msg = t!("game.created");

// With interpolation
let msg = t!("game.move_made", from = "e2", to = "e4");

Locale Resolution

1. --lang CLI flag
2. CHECKAI_LANG environment variable
3. System locale (auto-detected via sys-locale)
4. Fallback: English

Per-Request Locale (API)

API requests can specify a locale:

# Query parameter
GET /api/games?lang=de

# Accept-Language header
GET /api/games
Accept-Language: de

Frontend (Web UI)

The web frontend has its own translation module at web/src/i18n.ts with ~120 keys per language embedded inline.

Features

• Auto-detection from browser navigator.language
• Language selector dropdown in the header (dynamically populated)
• Persistence via localStorage (key: checkai-locale)
• data-i18n attributes for declarative HTML translations
• data-i18n-placeholder and data-i18n-title for inputs and tooltips
• t() function for programmatic access with %{name} interpolation

Adding a New Language

To add a new language (e.g. Italian):

1. Backend — add a YAML locale file:

Create locales/it.yml following the structure of locales/en.yml:

it:
  game.created: "Nuova partita creata. Il Bianco muove."
  game.move_made: "Mossa da %{from} a %{to}"
  # ... translate all keys from en.yml

The rust-i18n crate picks up new YAML files automatically.

2. Frontend — add translations to the DICTIONARIES object:

In web/src/i18n.ts, add a new entry:

it: {
  'app.title': 'CheckAI — Scacchi per agenti IA',
  'nav.dashboard': 'Pannello',
  // ... translate all keys
},

3. Register the locale in SUPPORTED_LOCALES:

export const SUPPORTED_LOCALES: LocaleInfo[] = [
  // ...existing locales
  { code: 'it', name: 'Italiano' },
];

The language selector will automatically include the new language.