# @intlify/h3

> Internationalization for H3

Latest version **2.1.2** (published 2026-04-08) · MIT license · 0 weekly downloads

## Install

```sh
npm install @intlify/h3
pnpm add @intlify/h3
yarn add @intlify/h3
bun add @intlify/h3
```

## Health

**Score 65/100 (B)** — status: stable.

Positive: has types; esm support; no vulnerabilities; has provenance; high maintenance score.

Warnings: low downloads.

## Facts

| | |
|---|---|
| Version | 2.1.2 |
| Published | 2026-04-08 |
| First published | 2023-09-16 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Node | >= 20 |
| Dependencies | 2 |
| Unpacked size | 44.7 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Provenance | attested (GitHub Actions) |
| GitHub stars | 13 |
| Author | kazuya kawaguchi |
| Maintainers | kazupon, ota-meshi |
| Keywords | i18n, h3, internationalization, intlify, utilities, middleware |

## Links

- npm: https://www.npmjs.com/package/@intlify/h3
- Repository: https://github.com/intlify/srvmid
- Homepage: https://github.com/intlify/srvmid/packages/h3#readme
- Issues: https://github.com/intlify/srvmid/issues
- Funding: https://github.com/sponsors/kazupon
- npm.io page: https://npm.io/package/@intlify/h3

## Dependencies (2)

- [@intlify/core](https://npm.io/package/@intlify/core.md) ^11.3.2
- [@intlify/utils](https://npm.io/package/@intlify/utils.md) ^1.0.1

## Recent versions

- 2.1.2 (latest) — 2026-04-08
- 3.0.0-beta.1 (next) — 2026-05-24
- 2.0.0-beta.1 (alpha) — 2025-11-21
- 2.1.1 — 2026-04-08
- 2.1.0 — 2026-04-05
- 2.0.0 — 2025-11-21
- 2.0.0-alpha.7 — 2025-11-18
- 2.0.0-alpha.6 — 2025-11-18
- 2.0.0-alpha.3 — 2025-11-14
- 1.0.0 — 2025-11-01
- 0.7.4 — 2025-11-01
- 0.7.1 — 2025-07-21
- 0.6.1 — 2024-11-19
- 0.6.0 — 2024-10-07
- 0.5.0 — 2023-12-06
- … 13 more at https://npm.io/package/@intlify/h3/versions

## README

<p align="center">
	<img alt="logo" width="512" src="./assets/intlify-h3.svg">
</p>
<h1 align="center">@intlify/h3</h1>

[![npm version][npm-version-src]][npm-version-href]
[![npm downloads][npm-downloads-src]][npm-downloads-href]
[![CI][ci-src]][ci-href]

Internationalization for H3

<!-- eslint-disable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

> [!NOTE]
> You’re viewing the `srvmid` repository, which is developing for H3 v2. If you want to check H3 v1, please see the [`@intlify/h3` repository](https://github.com/intlify/h3/tree/main)

<!-- eslint-enable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

## 🌟 Features

✅️️ &nbsp;**Internationalization utils:** support [internationalization
utils](https://github.com/intlify/srvmid/blob/main/packages/h3/docs/index.md) via [@intlify/utils](https://github.com/intlify/utils)

✅️ &nbsp;**Translation:** Simple API like
[vue-i18n](https://vue-i18n.intlify.dev/)

✅ &nbsp;**Custom locale detector:** You can implement your own locale detector
on server-side

## 💿 Installation

```sh
# Using npm
npm install @intlify/h3

# Using yarn
yarn add @intlify/h3

# Using pnpm
pnpm add @intlify/h3

# Using bun
bun add @intlify/h3
```

## 🚀 Usage

### Detect locale with utils

Detect locale from `accept-language` header:

```ts
import { H3 } from 'h3'
import { getHeaderLocale } from '@intlify/h3'

const app = new H3()

app.get('/', event => {
  // detect locale from HTTP header which has `Accept-Language: ja,en-US;q=0.7,en;q=0.3`
  const locale = getHeaderLocale(event.req)
  return locale.toString()
})
```

Detect locale from URL query:

```ts
import { H3 } from 'h3'
import { getQueryLocale } from '@intlify/h3'

const app = new H3()

app.get('/', event => {
  // detect locale from query which has 'http://localhost:3000?locale=en'
  const locale = getQueryLocale(event.req)
  return locale.toString()
})
```

### Translation

If you want to use translation, you need to install `intlify` plugin. As a result, you can use `useTranslation` within the handler:

```ts
import { createServer } from 'node:http'
import { H3, toNodeListener } from 'h3'
import { intlify, detectLocaleFromAcceptLanguageHeader, useTranslation } from '@intlify/h3'

// install `intlify` plugin with `H3` constructor
const app = new H3({
  plugins: [
    // configure plugin options
    intlify({
      // detect locale with `accept-language` header
      locale: detectLocaleFromAcceptLanguageHeader,
      // resource messages
      messages: {
        en: {
          hello: 'Hello {name}!'
        },
        ja: {
          hello: 'こんにちは、{name}！'
        }
      }
      // something options
      // ...
    })
  ]
})

app.get('/', async event => {
  // use `useTranslation` in event handler
  const t = await useTranslation(event)
  return t('hello', { name: 'h3' })
})

createServer(toNodeListener(app)).listen(3000)
```

## 🛠️ Custom locale detection

You can detect locale with your custom logic from current `H3Event`.

example for detecting locale from url query, and get locale with `getDetectorLocale` util:

```ts
import { H3 } from 'h3'
import { intlify, getQueryLocale, getDetectorLocale } from '@intlify/h3'

import type { H3Event } from 'h3'

// define custom locale detector
const localeDetector = (event: H3Event): string => {
  return getQueryLocale(event.req).toString()
}

const app = new H3({
  plugins: [
    intlify({
      // set your custom locale detector
      locale: localeDetector
      // something options
      // ...
    })
  ]
})

app.get('/', async event => {
  const locale = await getDetectorLocale(event)
  console.log(`Current Locale: ${locale.language}`)
})
```

You can make that function asynchronous. This is useful when loading resources along with locale detection.

<!-- eslint-disable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

> [!NOTE]
> The case which a synchronous function returns a promise is not supported. you need to use `async function`.

<!-- eslint-enable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

```ts
import { H3 } from 'h3'
import { intlify, getCookieLocale } from '@intlify/h3'

import type { H3Event } from 'h3'
import type { DefineLocaleMessage, CoreContext } from '@intlify/h3'

const loader = (path: string) => import(path).then(m => m.default)
const messages: Record<string, () => ReturnType<typeof loader>> = {
  en: () => loader('./locales/en.json'),
  ja: () => loader('./locales/ja.json')
}

// define custom locale detector and lazy loading
const localeDetector = async (
  event: H3Event,
  intlify: CoreContext<string, DefineLocaleMessage>
): Promise<string> => {
  // detect locale
  const locale = getCookieLocale(event.req).toString()

  // resource lazy loading
  const loader = messages[locale]
  if (loader && !intlify.messages[locale]) {
    const message = await loader()
    intlify.messages[locale] = message
  }

  return locale
}

const app = new H3({
  plugins: [
    intlify({
      // set your custom locale detector
      locale: localeDetector
      // something options
      // ...
    })
  ]
})
```

## 🖌️ Resource keys completion

<!-- eslint-disable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

> [!NOTE]
> Resource Keys completion can be used if you are using [Visual Studio Code](https://code.visualstudio.com/)

<!-- eslint-enable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

You can completion resources key on translation function with `useTranslation`.

![Key Completion](assets/key-completion.gif)

resource keys completion has two ways.

### Type parameter for `useTranslation`

<!-- eslint-disable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

> [!NOTE]
> The exeample code is [here](https://github.com/intlify/h3/tree/main/playground/local-schema)

<!-- eslint-enable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

You can `useTranslation` set the type parameter to the resource schema you want to key completion of the translation function.

the part of example:

```ts
app.get('/', async event => {
  type ResourceSchema = {
    hello: string
  }
  // set resource schema as type parameter
  const t = await useTranslation<ResourceSchema>(event)
  // you can completion when you type `t('`
  return t('hello', { name: 'h3' })
})
```

### global resource schema with `declare module '@intlify/h3'`

<!-- eslint-disable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

> [!NOTE]
> The exeample code is [here](https://github.com/intlify/h3/tree/main/playground/global-schema)

<!-- eslint-enable markdown/no-missing-label-refs -- NOTE(kazupon): ignore github alert -->

You can do resource key completion with the translation function using the typescript `declare module`.

the part of example:

```ts
import en from './locales/en.ts'

// 'en' resource is master schema
type ResourceSchema = typeof en

// you can put the type extending with `declare module` as global resource schema
declare module '@intlify/h3' {
  // extend `DefineLocaleMessage` with `ResourceSchema`
  export interface DefineLocaleMessage extends ResourceSchema {}
}

app.get('/', async event => {
  const t = await useTranslation(event)
  // you can completion when you type `t('`
  return t('hello', { name: 'h3' })
})
```

The advantage of this way is that it is not necessary to specify the resource schema in the `useTranslation` type parameter.

## 🛠️ Utilities & Helpers

`@intlify/h3` has a concept of composable utilities & helpers.

See the [API References](https://github.com/intlify/srvmid/blob/main/packages/h3/docs/index.md)

## 🙌 Contributing guidelines

If you are interested in contributing to `@intlify/h3`, I highly recommend checking out [the contributing guidelines](https://github.com/intlify/srvmid/blob/main/CONTRIBUTING.md) here. You'll find all the relevant information such as [how to make a PR](https://github.com/intlify/srvmid/blob/main/CONTRIBUTING.md#pull-request-guidelines), [how to setup development](https://github.com/intlify/srvmid/blob/main/CONTRIBUTING.md#development-setup)) etc., there.

## 🤝 Sponsors

The development of `srvmid` is supported by my OSS sponsors!

<p align="center">
  <a href="https://cdn.jsdelivr.net/gh/kazupon/sponsors/sponsors.svg">
    <img alt="sponsor" src='https://cdn.jsdelivr.net/gh/kazupon/sponsors/sponsors.svg'/>
  </a>
</p>

## ©️ License

[MIT](http://opensource.org/licenses/MIT)

<!-- Badges -->

[npm-version-src]: https://img.shields.io/npm/v/@intlify/h3?style=flat&colorA=18181B&colorB=FFAD33
[npm-version-href]: https://npmjs.com/package/@intlify/h3
[npm-downloads-src]: https://img.shields.io/npm/dm/@intlify/h3?style=flat&colorA=18181B&colorB=FFAD33
[npm-downloads-href]: https://npmjs.com/package/@intlify/h3
[ci-src]: https://github.com/intlify/srvmid/actions/workflows/ci.yml/badge.svg
[ci-href]: https://github.com/intlify/srvmid/actions/workflows/ci.yml

---
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