DEN": "Bạn không có quyền truy cập"
}
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**vi/response.json:**
{
"LOGIN_SUCCESS": "Đăng nhập thành công",
"REGISTER_SUCCESS": "Đăng ký thành công",
"LOGOUT_SUCCESS": "Đăng xuất thành công"
}
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## [](#3-register-i18nmodule)3\. Register I18nModule
// app.module.ts
import { I18nModule, HeaderResolver } from 'nestjs-i18n';
import * as path from 'path';
@Module({
imports: [
I18nModule.forRoot({
fallbackLanguage: 'vi',
loaderOptions: {
path: path.join(__dirname, '/i18n/'),
watch: true,
},
resolvers: [new HeaderResolver(['accept-language'])],
}),
// ... other imports
],
})
export class AppModule {}
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## [](#4-use-in-exception-filters)4\. Use in exception filters
// http-exception.filter.ts
import { I18nContext } from 'nestjs-i18n';
@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
catch(exception: HttpException, host: ArgumentsHost) {
const ctx = host.switchToHttp();
const i18n = I18nContext.current();
const response = ctx.getResponse<Response>();
const status = exception.getStatus();
const message = exception.message;
// Translate if the message is a dot-notation key like "validation.EMAIL_INVALID"
const translated = i18n?.translate(message) ?? message;
response.status(status).json({
statusCode: status,
message: translated,
timestamp: new Date().toISOString(),
});
}
}
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## [](#5-autodetect-language-from-headers)5\. Auto-detect language from headers
The `Accept-Language` header resolver does this automatically. The frontend sends `Accept-Language: vi` or `en` — NestJS picks it up. Zero extra code.
## [](#vietnamesespecific-gotchas)Vietnamese-specific gotchas
- **Tone marks**: `nest-i18n` stores JSON as UTF-8. Vietnamese characters (ắ, ễ, ở) work natively. No special handling needed.
- **Polite phrasing**: Vietnamese error messages should sound respectful. "Vui lòng nhập email" (Please enter email) not "Nhập email" (Enter email).
- **Placeholders**: Use `{min}` and `{max}` — they work with nestjs-i18n's interpolation:
"NAME_LENGTH": "Tên phải có từ {min} đến {max} ký tự"
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That's it. Your NestJS API now speaks Vietnamese natively.
* * *
_If you don't want to set this up from scratch, I built a [NestJS Vietnam Starter Kit](https://fadow.gumroad.com/l/nestjs-starter-kit-vietnam) with i18n, JWT auth, RBAC, Docker, and 36 tests — ready to go._
