---
createdAt: 2025-09-09
updatedAt: 2025-09-09
title: How to translate your Tanstack Start app – i18n guide 2025
description: Learn how to add internationalization (i18n) to your Tanstack Start application using Intlayer. Follow this comprehensive guide to make your app multilingual with locale-aware routing.
keywords:
  - Internationalization
  - Documentation
  - Intlayer
  - Tanstack Start
  - React
  - i18n
  - TypeScript
  - Locale Routing
slugs:
  - doc
  - environment
  - tanstack-start
applicationTemplate: https://github.com/aymericzip/intlayer-tanstack-start-template
history:
  - version: 6.5.2
    date: 2025-10-03
    changes: Update doc
  - version: 5.8.1
    date: 2025-09-09
    changes: Added for Tanstack Start
---

# Translate your Tanstack Start website using Intlayer | Internationalization (i18n)

## Table of Contents

<TOC/>

This guide demonstrates how to integrate **Intlayer** for seamless internationalization in Tanstack Start projects with locale-aware routing, TypeScript support, and modern development practices.

## What is Intlayer?

**Intlayer** is an innovative, open-source internationalization (i18n) library designed to simplify multilingual support in modern web applications.

With Intlayer, you can:

- **Easily manage translations** using declarative dictionaries at the component level.
- **Dynamically localize metadata**, routes, and content.
- **Ensure TypeScript support** with autogenerated types, improving autocompletion and error detection.
- **Benefit from advanced features**, like dynamic locale detection and switching.
- **Enable locale-aware routing** with Tanstack Start's file-based routing system.

---

## Step-by-Step Guide to Set Up Intlayer in a Tanstack Start Application

### Step 1: Create Project

Start by creating a new TanStack Start project by following the [Start new project](https://tanstack.com/start/latest/docs/framework/react/quick-start) guide on the TanStack Start website.

### Step 2: Install Intlayer Packages

Install the necessary packages using your preferred package manager:

```bash packageManager="npm"
npm install intlayer react-intlayer
npm install vite-intlayer --save-dev
```

```bash packageManager="pnpm"
pnpm add intlayer react-intlayer
pnpm add vite-intlayer --save-dev
```

- **intlayer**

  The core package that provides internationalization tools for configuration management, translation, [content declaration](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/dictionary/content_file.md), transpilation, and [CLI commands](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/intlayer_cli.md).

- **react-intlayer**
  The package that integrates Intlayer with React application. It provides context providers and hooks for React internationalization.

- **vite-intlayer**
  Includes the Vite plugin for integrating Intlayer with the [Vite bundler](https://vite.dev/guide/why.html#why-bundle-for-production), as well as middleware for detecting the user's preferred locale, managing cookies, and handling URL redirection.

### Step 3: Configuration of your project

Create a config file to configure the languages of your application:

```typescript fileName="intlayer.config.ts"
import type { IntlayerConfig } from "intlayer";

import { Locales } from "intlayer";

const config: IntlayerConfig = {
  internationalization: {
    defaultLocale: Locales.ENGLISH,
    locales: [Locales.ENGLISH, Locales.FRENCH, Locales.SPANISH],
  },
};

export default config;
```

> Through this configuration file, you can set up localized URLs, middleware redirection, cookie names, the location and extension of your content declarations, disable Intlayer logs in the console, and more. For a complete list of available parameters, refer to the [configuration documentation](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/configuration.md).

### Step 4: Integrate Intlayer in Your Vite Configuration

Add the intlayer plugin into your configuration:

```typescript fileName="vite.config.ts"
import { reactRouter } from "@react-router/dev/vite";
import { defineConfig } from "vite";
import { intlayer } from "vite-intlayer";
import tsconfigPaths from "vite-tsconfig-paths";

export default defineConfig({
  plugins: [reactRouter(), tsconfigPaths(), intlayer()],
});
```

> The `intlayer()` Vite plugin is used to integrate Intlayer with Vite. It ensures the building of content declaration files and monitors them in development mode. It defines Intlayer environment variables within the Vite application. Additionally, it provides aliases to optimize performance.

### Step 5: Create Layout Components

Set up your root layout and locale-specific layouts:

#### Root Layout

```tsx fileName="src/routes/{-$locale}/route.tsx"
import { createFileRoute, Navigate, Outlet } from "@tanstack/react-router";
import { IntlayerProvider, useLocale } from "react-intlayer";

import { useI18nHTMLAttributes } from "@/hooks/useI18nHTMLAttributes";

export const Route = createFileRoute("/{-$locale}")({
  component: LayoutComponent,
});

function LayoutComponent() {
  const { defaultLocale } = useLocale();
  const { locale } = Route.useParams();

  return (
    <IntlayerProvider locale={defaultLocale}>
      <Outlet />
    </IntlayerProvider>
  );
}
```

### Step 6: Declare Your Content

Create and manage your content declarations to store translations:

```tsx fileName="src/contents/page.content.ts"
import type { Dictionary } from "intlayer";

import { t } from "intlayer";

const appContent = {
  content: {
    links: {
      about: t({
        en: "About",
        es: "Acerca de",
        fr: "À propos",
      }),
      home: t({
        en: "Home",
        es: "Inicio",
        fr: "Accueil",
      }),
    },
    meta: {
      description: t({
        en: "This is an example of using Intlayer with TanStack Router",
        es: "Este es un ejemplo de uso de Intlayer con TanStack Router",
        fr: "Ceci est un exemple d'utilisation d'Intlayer avec TanStack Router",
      }),
    },
    title: t({
      en: "Welcome to Intlayer + TanStack Router",
      es: "Bienvenido a Intlayer + TanStack Router",
      fr: "Bienvenue à Intlayer + TanStack Router",
    }),
  },
  key: "app",
} satisfies Dictionary;

export default appContent;
```

> Your content declarations can be defined anywhere in your application as soon they are included into the `contentDir` directory (by default, `./app`). And match the content declaration file extension (by default, `.content.{json,ts,tsx,js,jsx,mjs,mjx,cjs,cjx}`).

> For more details, refer to the [content declaration documentation](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/dictionary/content_file.md).

### Step 7: Create Locale-Aware Components and Hooks

Create a `LocalizedLink` component for locale-aware navigation:

```tsx fileName="src/components/localized-link.tsx"
import type { FC } from "react";

import { Link, type LinkComponentProps } from "@tanstack/react-router";
import { useLocale } from "react-intlayer";

export const LOCALE_ROUTE = "{-$locale}" as const;

// Main utility
export type RemoveLocaleParam<T> = T extends string
  ? RemoveLocaleFromString<T>
  : T;

export type To = RemoveLocaleParam<LinkComponentProps["to"]>;

type CollapseDoubleSlashes<S extends string> =
  S extends `${infer H}//${infer T}` ? CollapseDoubleSlashes<`${H}/${T}`> : S;

type LocalizedLinkProps = {
  to?: To;
} & Omit<LinkComponentProps, "to">;

// Helpers
type RemoveAll<
  S extends string,
  Sub extends string,
> = S extends `${infer H}${Sub}${infer T}` ? RemoveAll<`${H}${T}`, Sub> : S;

type RemoveLocaleFromString<S extends string> = CollapseDoubleSlashes<
  RemoveAll<S, typeof LOCALE_ROUTE>
>;

export const LocalizedLink: FC<LocalizedLinkProps> = (props) => {
  const { locale } = useLocale();

  return (
    <Link
      {...props}
      params={{
        locale,
        ...(typeof props?.params === "object" ? props?.params : {}),
      }}
      to={`/${LOCALE_ROUTE}${props.to}` as LinkComponentProps["to"]}
    />
  );
};
```

This component has two objectives:

- Remove the unnecessary `{-$locale}` prefix from the URL.
- Inject the locale parameter into the URL to ensure the user is directly redirected to the localized route.

Then we can create a `useLocalizedNavigate` hook for programmatic navigation:

```tsx fileName="src/hooks/useLocalizedNavigate.tsx"
import { useLocale } from "react-intlayer";
import { useNavigate } from "@tanstack/react-router";
import { LOCALE_ROUTE } from "@/components/localized-link";
import type { FileRouteTypes } from "@/routeTree.gen";

export const useLocalizedNavigate = () => {
  const navigate = useNavigate();

  const { locale } = useLocale();

  type StripLocalePrefix<T extends string> = T extends
    | `/${typeof LOCALE_ROUTE}`
    | `/${typeof LOCALE_ROUTE}/`
    ? "/"
    : T extends `/${typeof LOCALE_ROUTE}/${infer Rest}`
      ? `/${Rest}`
      : never;

  type LocalizedTo = StripLocalePrefix<FileRouteTypes["to"]>;

  interface LocalizedNavigate {
    (to: LocalizedTo): ReturnType<typeof navigate>;
    (
      opts: { to: LocalizedTo } & Record<string, unknown>
    ): ReturnType<typeof navigate>;
  }

  const localizedNavigate: LocalizedNavigate = (args: any) => {
    if (typeof args === "string") {
      return navigate({ to: `/${LOCALE_ROUTE}${args}`, params: { locale } });
    }

    const { to, ...rest } = args;

    const localedTo = `/${LOCALE_ROUTE}${to}` as any;

    return navigate({ to: localedTo, params: { locale, ...rest } as any });
  };

  return localizedNavigate;
};
```

### Step 8: Utilize Intlayer in Your Pages

Access your content dictionaries throughout your application:

#### Localized Home Page

```tsx fileName="src/routes/{-$locale}/index.tsx"
import { createFileRoute } from "@tanstack/react-router";
import { getIntlayer } from "intlayer";
import { useIntlayer } from "react-intlayer";

import LocaleSwitcher from "@/components/locale-switcher";
import { LocalizedLink } from "@/components/localized-link";
import { useLocalizedNavigate } from "@/hooks/useLocalizedNavigate";

export const Route = createFileRoute("/{-$locale}/")({
  component: RouteComponent,
  head: ({ params }) => {
    const { locale } = params;
    const metaContent = getIntlayer("app", locale);

    return {
      meta: [
        { title: metaContent.title },
        { content: metaContent.meta.description, name: "description" },
      ],
    };
  },
});

function RouteComponent() {
  const content = useIntlayer("app");
  const navigate = useLocalizedNavigate();

  return (
    <div>
      <div>
        {content.title}
        <LocaleSwitcher />
        <div>
          <LocalizedLink to="/">{content.links.home}</LocalizedLink>
          <LocalizedLink to="/about">{content.links.about}</LocalizedLink>
        </div>
        <div>
          <button onClick={() => navigate({ to: "/" })}>
            {content.links.home}
          </button>
          <button onClick={() => navigate({ to: "/about" })}>
            {content.links.about}
          </button>
        </div>
      </div>
    </div>
  );
}
```

> To Learn more about the `useIntlayer` hook, refer to the [documentation](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/packages/react-intlayer/useIntlayer.md).

### Step 9: Create a Locale Switcher Component

Create a component to allow users to change languages:

```tsx fileName="src/components/locale-switcher.tsx"
import type { FC } from "react";

import { useLocation } from "@tanstack/react-router";
import { getHTMLTextDir, getLocaleName, getPathWithoutLocale } from "intlayer";
import { setLocaleCookie, useIntlayer, useLocale } from "react-intlayer";

import { LocalizedLink, To } from "./localized-link";

export const LocaleSwitcher: FC = () => {
  const { localeSwitcherLabel } = useIntlayer("locale-switcher");
  const { pathname } = useLocation();

  const { availableLocales, locale } = useLocale();

  const pathWithoutLocale = getPathWithoutLocale(pathname);

  return (
    <ol>
      {availableLocales.map((localeEl) => (
        <li key={localeEl}>
          <LocalizedLink
            aria-current={localeEl === locale ? "page" : undefined}
            aria-label={`${localeSwitcherLabel.value} ${getLocaleName(localeEl)}`}
            onClick={() => setLocaleCookie(localeEl)}
            params={{ locale: localeEl }}
            to={pathWithoutLocale as To}
          >
            <span>
              {/* Locale - e.g. FR */}
              {localeItem}
            </span>
            <span>
              {/* Language in its own Locale - e.g. Français */}
              {getLocaleName(localeItem, locale)}
            </span>
            <span dir={getHTMLTextDir(localeItem)} lang={localeItem}>
              {/* Language in current Locale - e.g. Francés with current locale set to Locales.SPANISH */}
              {getLocaleName(localeItem)}
            </span>
            <span dir="ltr" lang={Locales.ENGLISH}>
              {/* Language in English - e.g. French */}
              {getLocaleName(localeItem, Locales.ENGLISH)}
            </span>
          </LocalizedLink>
        </li>
      ))}
    </ol>
  );
};
```

> To Learn more about the `useLocale` hook, refer to the [documentation](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/packages/react-intlayer/useLocale.md).

### Step 10: Add HTML Attributes Management (Optional)

Create a hook to manage HTML lang and dir attributes:

```tsx fileName="src/hooks/useI18nHTMLAttributes.tsx"
// src/hooks/useI18nHTMLAttributes.tsx
import { getHTMLTextDir } from "intlayer";
import { useEffect } from "react";
import { useLocale } from "react-intlayer";

export const useI18nHTMLAttributes = () => {
  const { locale } = useLocale();

  useEffect(() => {
    document.documentElement.lang = locale;
    document.documentElement.dir = getHTMLTextDir(locale);
  }, [locale]);
};
```

Then use it in your root component:

```tsx fileName="src/routes/{-$locale}/index.tsx"
import { createFileRoute, Navigate, Outlet } from "@tanstack/react-router";
import { IntlayerProvider, useLocale } from "react-intlayer";

import { useI18nHTMLAttributes } from "@/hooks/useI18nHTMLAttributes"; // import the hook

export const Route = createFileRoute("/{-$locale}")({
  component: LayoutComponent,
});

function LayoutComponent() {
  useI18nHTMLAttributes(); // add this line

  const { defaultLocale } = useLocale();
  const { locale } = Route.useParams();

  return (
    <IntlayerProvider locale={locale ?? defaultLocale}>
      <Outlet />
    </IntlayerProvider>
  );
}
```

---

### Step 11: Add middleware (Optional)

You can also use the `intlayerMiddleware` to add server-side routing to your application. This plugin will automatically detect the current locale based on the URL and set the appropriate locale cookie. If no locale is specified, the plugin will determine the most appropriate locale based on the user's browser language preferences. If no locale is detected, it will redirect to the default locale.

> Note that to use the `intlayerMiddleware` in production, you need to switch the `vite-intlayer` package from `devDependencies` to `dependencies`.

```typescript {3,7} fileName="vite.config.ts"
import { reactRouter } from "@react-router/dev/vite";
import tailwindcss from "@tailwindcss/vite";
import { defineConfig } from "vite";
import { intlayer, intlayerMiddleware } from "vite-intlayer";
import tsconfigPaths from "vite-tsconfig-paths";

export default defineConfig({
  plugins: [
    tailwindcss(),
    reactRouter(),
    tsconfigPaths(),
    intlayer(),
    intlayerMiddleware(),
  ],
});
```

---

### Step 12: Configure TypeScript (Optional)

Intlayer uses module augmentation to get benefits of TypeScript and make your codebase stronger.

Ensure your TypeScript configuration includes the autogenerated types:

```json5 fileName="tsconfig.json"
{
  // ... your existing configurations
  include: [
    // ... your existing includes
    ".intlayer/**/*.ts", // Include the auto-generated types
  ],
}
```

---

### Git Configuration

It is recommended to ignore the files generated by Intlayer. This allows you to avoid committing them to your Git repository.

To do this, you can add the following instructions to your `.gitignore` file:

```plaintext fileName=".gitignore"
# Ignore the files generated by Intlayer
.intlayer
```

---

## VS Code Extension

To improve your development experience with Intlayer, you can install the official **Intlayer VS Code Extension**.

[Install from the VS Code Marketplace](https://marketplace.visualstudio.com/items?itemName=intlayer.intlayer-vs-code-extension)

This extension provides:

- **Autocompletion** for translation keys.
- **Real-time error detection** for missing translations.
- **Inline previews** of translated content.
- **Quick actions** to easily create and update translations.

For more details on how to use the extension, refer to the [Intlayer VS Code Extension documentation](https://intlayer.org/doc/vs-code-extension).

---

## Go Further

To go further, you can implement the [visual editor](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/intlayer_visual_editor.md) or externalize your content using the [CMS](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/intlayer_CMS.md).

---

## Documentation References

- [Intlayer Documentation](https://intlayer.org)
- [Tanstack Start Documentation](https://reactrouter.com/)
- [useIntlayer hook](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/packages/react-intlayer/useIntlayer.md)
- [useLocale hook](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/packages/react-intlayer/useLocale.md)
- [Content Declaration](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/dictionary/content_file.md)
- [Configuration](https://github.com/aymericzip/intlayer/blob/main/docs/docs/en/configuration.md)

This comprehensive guide provides everything you need to integrate Intlayer with Tanstack Start for a fully internationalized application with locale-aware routing and TypeScript support.
