How to Set Up i18n in NestJS — with Vietnamese Translations

Most i18n tutorials stop at English and Spanish. If you're building for Vietnamese users, you need proper tone marks, natural phrasing, and a setup that doesn't fight you. Here's how I built a NestJS i18n system that auto-detects Accept-Language and returns error messages in Vietnamese or English. 1. Install nestjs-i18n npm install nestjs-i18n Enter fullscreen mode Exit fullscreen mode 2. Create translation files src/i18n/ ├── vi/ │ ├── validation.json │ └── response.json └── en/ ├── validation.json └── response.json Enter fullscreen mode Exit fullscreen mode vi/validation.json: { "EMAIL_INVALID": "Email không hợp lệ", "PASSWORD_MIN_LENGTH": "Mật khẩu phải có ít nhất 6 ký tự", "USER_NOT_FOUND": "Không tìm thấy người dùng", "EMAIL_EXISTS": "Email đã tồn tại", "FORBIDDEN": "Bạn không có quyền truy cập" } Enter fullscreen mode Exit fullscreen mode vi/response.json: { "LOGIN_SUCCESS": "Đăng nhập thành công", "REGISTER_SUCCESS": "Đăng ký thành công", "LOGOUT_SUCCESS": "Đăng xuất thành công" } Enter fullscreen mode Exit fullscreen mode 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 {} Enter fullscreen mode Exit fullscreen mode 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(); 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(), }); } } Enter fullscreen mode Exit fullscreen mode 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. 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" Enter fullscreen mode Exit fullscreen mode 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 with i18n, JWT auth, RBAC, Docker, and 36 tests — ready to go.