A Chrome extension that forces the browser locale to Japanese (ja).

localeja modifies the browser locale in two ways:

• Accept-Language HTTP header: Rewrites the Accept-Language header to ja,en-US;q=0.9,en;q=0.8 for all requests using the declarativeNetRequest API (server-side locale detection).
• navigator.language / navigator.languages: Overrides navigator.language to "ja" and navigator.languages to ["ja", "en-US", "en"] via a MAIN world content script (client-side locale detection).

1. Clone this repository
2. Install dependencies: pnpm install
3. Build the extension: pnpm build
4. Open chrome://extensions/ in Chrome
5. Enable "Developer mode"
6. Click "Load unpacked" and select the dist/ directory

pnpm dev          # Build with watch mode
pnpm build        # Production build
pnpm typecheck    # Run TypeScript type checking
pnpm lint         # Run linter (oxlint)
pnpm format       # Format code (prettier)
pnpm package      # Build and create package.zip

MIT