# LanguageVariables

**Kind:** Interface

**Source:** [`src/middleware/language/language.ts`](https://github.com/honojs/hono/blob/main/src/middleware/language/language.ts#L47)

**Part of:** [Middleware](subsystem-src-middleware)

`LanguageVariables` defines the language value used by language middleware. It carries a `language` string so downstream middleware or handlers can read the active language.

## Properties

| Property | Type |
|---|---|
| `language` | `string` |

## Diagram

```mermaid
graph LR
  A[Language middleware] --> B[LanguageVariables]
  B --> C[language: string]
  B --> D[Downstream middleware or handlers]
```

## Usage

```ts
import type { LanguageVariables } from './src/middleware/language/language';

const variables: LanguageVariables = {
  language: 'en',
};

function getLanguage({ language }: LanguageVariables): string {
  return language;
}

const activeLanguage = getLanguage(variables);
```

## AI Coding Instructions

- Keep the `language` field as a string when creating `LanguageVariables` values.
- Pass `LanguageVariables` through middleware context or handler parameters where language state is needed.
- Do not rename the `language` property without updating middleware and downstream consumers.
- Validate or normalize language input before assigning it to this interface when input comes from requests.

## How it works

`LanguageVariables` is an exported TypeScript interface with one context-variable entry:

- `language: string` — the selected language value is typed as a string. [src/middleware/language/language.ts:47-49]

It is intended for the `Variables` type of a Hono application: the in-file example aliases `LanguageVariables` and passes it as `Variables` when constructing `Hono`. [src/middleware/language/language.ts:274-278] With that typing, `c.get('language')` refers to the `language` variable. [src/middleware/language/language.ts:286-289] Context variable getters and setters map keys in `E['Variables']` to their declared value types. [src/context.ts:95-108]

`LanguageVariables` itself has no methods, validation, errors, or runtime side effects. The related `languageDetector` middleware detects a language, stores it as `ctx.set('language', lang)`, then calls the next middleware. [src/middleware/language/language.ts:302-308] The stored value is either the first detected language from the configured detector order or `fallbackLanguage`. [src/middleware/language/language.ts:238-266]