Translate your Tanstack Start website using Intlayer | Internationalisation (i18n)

Table of Contents

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

Why Intlayer over alternatives?

Compared to main solutions like react-i18next or use-intl, or paraglide, Intlayer is a solution that comes with integrated optimizations such as:

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

See Application Template on GitHub.

1. 1

   Create Project

   Start by creating a new Tanstack Start project by following the Start new project guide on the Tanstack Start website.

2. 2

   Install Intlayer Packages

   Install the necessary packages using your preferred package manager:

   bash

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   npm install intlayer react-intlayernpm install vite-intlayer --save-devnpx intlayer init

   • intlayer

     The core package that provides internationalisation tools for configuration management, translation, content declaration, transpilation, and CLI commands.

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

   • vite-intlayer Includes the Vite plugin for integrating Intlayer with the Vite bundler, as well as middleware for detecting the user's preferred locale, managing cookies, and handling URL redirection.

3. 3

   Configuration of your project

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

   intlayer.config.ts

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   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 localised 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.

4. 4

   Integrate Intlayer in Your Vite Configuration

   Add the intlayer plugin into your configuration:

   vite.config.ts

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   import { tanstackStart } from "@tanstack/react-start/plugin/vite";import viteReact from "@vitejs/plugin-react";import { nitro } from "nitro/vite";import { defineConfig } from "vite";import { intlayer } from "vite-intlayer";const config = defineConfig({  plugins: [    nitro(),    intlayer(),    tanstackStart({      router: {        routeFileIgnorePattern:          ".content.(ts|tsx|js|mjs|cjs|jsx|json|jsonc|json5)$",      },    }),    viteReact(),  ],});export default config;

   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 optimise performance.

5. 5

   Create Root Layout

   Configure your root layout to support internationalisation by using useParams to detect the current locale and setting the lang and dir attributes on the html tag.

   src/routes/__root.tsx

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   import {  createRootRouteWithContext,  HeadContent,  Scripts,} from "@tanstack/react-router";import { defaultLocale, getHTMLTextDir } from "intlayer";import { type ReactNode } from "react";import { IntlayerProvider } from "react-intlayer";import { Route as LocaleRoute } from "./{-$locale}/route";export const Route = createRootRouteWithContext<{}>()({  head: () => ({    meta: [      {        charSet: "utf-8",      },      {        content: "width=device-width, initial-scale=1",        name: "viewport",      },      {        title: "TanStack Start Starter",      },    ],  }),  shellComponent: RootDocument,});function RootDocument({ children }: { children: ReactNode }) {  const params = LocaleRoute.useParams();  const locale = params?.locale ?? defaultLocale;  return (    <html dir={getHTMLTextDir(locale)} lang={locale}>      <head>        <HeadContent />      </head>      <body>        <IntlayerProvider locale={locale}>{children}</IntlayerProvider>        <Scripts />      </body>    </html>  );}

   If you want to use your content in a string attribute, such as alt, title, href, aria-label, etc., you can use the value of the function, like:

   html

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   <img src="{content.image.src.value}" alt="{content.image.value}" /><img src="{content.image.src.toString()}" alt="{content.image.toString()}" /><img src="{String(content.image.src)}" alt="{String(content.image)}" />

6. 6

   Create Locale Layout

   Create a layout that handles the locale prefix and performs validation.

   src/routes/{-$locale}/route.tsx

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   import { createFileRoute, Outlet, redirect } from "@tanstack/react-router";import { validatePrefix } from "intlayer";export const Route = createFileRoute("/{-$locale}")({  beforeLoad: ({ params }) => {    const localeParam = params.locale;    // Validate the locale prefix    const { isValid, localePrefix } = validatePrefix(localeParam);    if (!isValid) {      throw redirect({        to: "/{-$locale}/404",        params: { locale: localePrefix },      });    }  },  component: Outlet,});

   Here, {-$locale} is a dynamic route parameter that gets replaced with the current locale. This notation makes the slot optional, allowing it to work with routing modes such as 'prefix-no-default' etc.

   Be aware that this slot may cause issues if you use multiple dynamic segments in the same route (e.g., /{-$locale}/other-path/$anotherDynamicPath/...). For the 'prefix-all' mode, you may prefer switching the slot to $locale instead. For the 'no-prefix' or 'search-params' mode, you can remove the slot entirely.

7. 7

   Declare Your Content

   Create and manage your content declarations to store translations:

   src/contents/page.content.ts

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   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: {      title: t({        en: "Welcome to Intlayer + TanStack Router",        es: "Bienvenido a Intlayer + TanStack Router",        fr: "Bienvenue à Intlayer + TanStack Router",      }),      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",      }),    },  },  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,cjs,md,mdx,yaml,yml}).

   For more details, refer to the content declaration documentation.

8. 8

   Create Locale-Aware Components and Hooks

   Create a LocalisedLink component for locale-aware navigation:

   src/components/localized-link.tsx

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   import type { FC } from "react";import { Link, type LinkComponentProps } from "@tanstack/react-router";import { useLocale } from "react-intlayer";import { getPrefix } from "intlayer";export const LOCALE_ROUTE = "{-$locale}" as const;export type To = StripLocalePrefix<LinkComponentProps["to"]>;export type StripLocalePrefix<T extends string | undefined> = T extends  | `/${typeof LOCALE_ROUTE}/`  | `/${typeof LOCALE_ROUTE}`  ? "/"  : T extends `/${typeof LOCALE_ROUTE}/${infer Rest}`    ? `/${Rest}`    : T;type LocalizedLinkProps = {  to?: To;} & Omit<LinkComponentProps, "to">;export const LocalizedLink: FC<LocalizedLinkProps> = (props) => {  const { locale } = useLocale();  const { localePrefix } = getPrefix(locale);  return (    <Link      {...props}      params={{        locale: localePrefix,        ...(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 localised route.

   Then we can create a useLocalizedNavigate hook for programmatic navigation:

   src/hooks/useLocalizedNavigate.tsx

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   import { useNavigate } from "@tanstack/react-router";import { getPrefix } from "intlayer";import { useLocale } from "react-intlayer";import type { StripLocalePrefix } from "@/components/localized-link";import type { FileRouteTypes } from "@/routeTree.gen";type NavigateFn = ReturnType<typeof useNavigate>;type BaseNavigateOptions = Parameters<NavigateFn>[0];type LocalizedTo = StripLocalePrefix<FileRouteTypes["to"]>;export type LocalizedNavigateOptions = Omit<  BaseNavigateOptions,  "to" | "params"> & {  to: LocalizedTo;  params?: Omit<NonNullable<BaseNavigateOptions["params"]>, "locale">;};type LocalizedNavigate = (  options: LocalizedNavigateOptions) => ReturnType<NavigateFn>;export const useLocalizedNavigate = () => {  const navigate = useNavigate();  const { locale } = useLocale();  const localizedNavigate: LocalizedNavigate = (args: any) => {    const { localePrefix } = getPrefix(locale);    if (typeof args === "string") {      return navigate({        to: `/${LOCALE_ROUTE}${args}`,        params: { locale: localePrefix },      });    }    const { to, ...rest } = args;    const localizedTo = `/${LOCALE_ROUTE}${to}` as any;    return navigate({      to: localizedTo,      params: { locale: localePrefix, ...rest } as any,    });  };  return localizedNavigate;};

9. 9

   Utilize Intlayer in Your Pages

   Access your content dictionaries throughout your application:

   Localised Home Page

   src/routes/{-$locale}/index.tsx

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   import { createFileRoute } from "@tanstack/react-router";import { getIntlayer } from "intlayer";import { useIntlayer } from "react-intlayer";import LocaleSwitcher from "@/components/locale-switcher";import { LocalisedLink } from "@/components/localized-link";import { useLocalizedNavigate } from "@/hooks/useLocalizedNavigate";export const Route = createFileRoute("/{-$locale}/")({  component: RouteComponent,});function RouteComponent() {  const content = useIntlayer("app");  const navigate = useLocalizedNavigate();  return (    <div>      <div>        {content.title}        <LocaleSwitcher />        <div>          <LocalisedLink to="/">{content.links.home}</LocalisedLink>          <LocalisedLink to="/about">{content.links.about}</LocalisedLink>        </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.

10. 10

    Create a Locale Switcher Component

    Create a component to allow users to change languages:

    src/components/locale-switcher.tsx

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    import { useLocation } from "@tanstack/react-router";import {  getHTMLTextDir,  getLocaleName,  getPathWithoutLocale,  getPrefix,  Locales,} from "intlayer";import type { FC } from "react";import { useLocale } from "react-intlayer";import { LocalisedLink, type To } from "./localized-link";export const LocaleSwitcher: FC = () => {  const { pathname } = useLocation();  const { availableLocales, locale, setLocale } = useLocale();  const pathWithoutLocale = getPathWithoutLocale(pathname);  return (    <ol>      {availableLocales.map((localeEl) => (        <li key={localeEl}>          <LocalisedLink            aria-current={localeEl === locale ? "page" : undefined}            onClick={() => setLocale(localeEl)}            params={{ locale: getPrefix(localeEl).localePrefix }}            to={pathWithoutLocale as To}          >            <span>              {/* Locale - e.g. FR */}              {localeEl}            </span>            <span>              {/* Language in its own Locale - e.g. Français */}              {getLocaleName(localeEl, locale)}            </span>            <span dir={getHTMLTextDir(localeEl)} lang={localeEl}>              {/* Language in current Locale - e.g. Francés with current locale set to Locales.SPANISH */}              {getLocaleName(localeEl)}            </span>            <span dir="ltr" lang={Locales.ENGLISH}>              {/* Language in English - e.g. French */}              {getLocaleName(localeEl, Locales.ENGLISH)}            </span>          </LocalisedLink>        </li>      ))}    </ol>  );};

    To Learn more about the useLocale hook, refer to the documentation.

11. 11

    HTML Attributes Management

    As seen in Step 5, you can manage the lang and dir attributes of the html tag using useParams in your root component. This ensures that the correct attributes are set on the server and client.

    src/routes/__root.tsx

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    function RootDocument({ children }: { children: ReactNode }) {  const params = LocaleRoute.useParams();  const locale = params?.locale ?? defaultLocale;  return (    <html dir={getHTMLTextDir(locale)} lang={locale}>      {/* ... */}    </html>  );}

    ---

12. 12

    Add middleware

    You can also use the intlayerProxy 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 intlayerProxy in production, you need to switch the vite-intlayer package from devDependencies to dependencies.

    vite.config.ts

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    import { tanstackStart } from "@tanstack/react-start/plugin/vite";import viteReact from "@vitejs/plugin-react";import { nitro } from "nitro/vite";import { defineConfig } from "vite";import { intlayer, intlayerProxy } from "vite-intlayer";export default defineConfig({  plugins: [    intlayerProxy(), // The proxy should be placed before server if you use Nitro    nitro(),    intlayer(),    tanstackStart({      router: {        routeFileIgnorePattern:          ".content.(ts|tsx|js|mjs|cjs|jsx|json|jsonc|json5)$",      },    }),    viteReact(),  ],});

    ---

13. 13

    Internationalise your Metadata

    You can also use the getIntlayer hook to access your content dictionaries throughout your application:

    src/routes/{-$locale}/index.tsx

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    import { createFileRoute } from "@tanstack/react-router";import { getIntlayer } from "intlayer";export const Route = createFileRoute("/{-$locale}/")({  component: RouteComponent,  head: ({ params }) => {    const { locale } = params;    const path = "/"; // The path for this route    const metaContent = getIntlayer("app", locale);    return {      links: [        // Canonical link: Points to the current localized page        { rel: "canonical", href: getLocalizedUrl(path, locale) },        // Hreflang: Tell Google about all localized versions        ...localeMap(({ locale: mapLocale }) => ({          rel: "alternate",          hrefLang: mapLocale,          href: getLocalizedUrl(path, mapLocale),        })),        // x-default: For users in unmatched languages        // Define the default fallback locale (usually your primary language)        {          rel: "alternate",          hrefLang: "x-default",          href: getLocalizedUrl(path, defaultLocale),        },      ],      meta: [        { title: metaContent.title },        { name: "description", content: metaContent.meta.description },      ],    };  },});

    ---

14. 14

    Retrieve the locale in your server actions

    You may want to access the current locale from inside your server actions or API endpoints. You can do this using the getLocale helper from intlayer.

    Here's an example using TanStack Start's server functions:

    src/routes/{-$locale}/index.tsx

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    import { createServerFn } from "@tanstack/react-start";import {  getRequestHeader,  getRequestHeaders,} from "@tanstack/react-start/server";import { getCookie, getIntlayer, getLocale } from "intlayer";export const getLocaleServer = createServerFn().handler(async () => {  const locale = await getLocale({    // Get the cookie from the request (default: 'INTLAYER_LOCALE')    getCookie: (name) => {      const cookieString = getRequestHeader("cookie");      return getCookie(name, cookieString);    },    // Get the header from the request (default: 'x-intlayer-locale')    // Fallback using Accept-Language negotiation    getHeader: (name) => getRequestHeader(name),  });  // Retrieve some content using getIntlayer()  const content = getIntlayer("app", locale);  return { locale, content };});

    ---

15. 15

    Manage not found pages

    When a user visits a non-existing page, you can display a custom not found page and the locale prefix may impact the way the not found page is triggered.

    Understanding TanStack Router's 404 Handling with Locale Prefixes

    In TanStack Router, handling 404 pages with localised routes requires a multi-layered approach:

    1. Dedicated 404 route: A specific route to display the 404 UI
    2. Route-level validation: Validates locale prefixes and redirects invalid ones to 404
    3. Catch-all route: Captures any unmatched paths within the locale segment

    src/routes/{-$locale}/404.tsx

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    import { createFileRoute } from "@tanstack/react-router";// This creates a dedicated /[locale]/404 route// It's used both as a direct route and imported as a component in other filesexport const Route = createFileRoute("/{-$locale}/404")({  component: NotFoundComponent,});// Exported separately so it can be reused in notFoundComponent and catch-all routesexport function NotFoundComponent() {  return (    <div>      <h1>404</h1>    </div>  );}

    src/routes/{-$locale}/route.tsx

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    import { createFileRoute, Outlet, redirect } from "@tanstack/react-router";import { validatePrefix } from "intlayer";import { NotFoundComponent } from "./404";export const Route = createFileRoute("/{-$locale}")({  // beforeLoad runs before the route renders (on both server and client)  // It's the ideal place to validate the locale prefix  beforeLoad: ({ params }) => {    const localeParam = params.locale;    // validatePrefix checks if the locale is valid according to your intlayer config    const { isValid, localePrefix } = validatePrefix(localeParam);    if (!isValid) {      // Invalid locale prefix - redirect to the 404 page with a valid locale prefix      throw redirect({        to: "/{-$locale}/404",        params: { locale: localePrefix },      });    }  },  component: Outlet,  // notFoundComponent is called when a child route doesn't exist  // e.g., /en/non-existent-page triggers this within the /en layout  notFoundComponent: NotFoundComponent,});

    src/routes/{-$locale}/$.tsx

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    import { createFileRoute } from "@tanstack/react-router";import { NotFoundComponent } from "./404";// The $ (splat/catch-all) route matches any path that doesn't match other routes// e.g., /en/some/deeply/nested/invalid/path// This ensures ALL unmatched paths within a locale show the 404 page// Without this, unmatched deep paths might show a blank page or errorexport const Route = createFileRoute("/{-$locale}/$")({  component: NotFoundComponent,});

    ---

16. 16

    Generate Sitemap

    Intlayer comes with a built-in sitemap generator to help you create a sitemap for your application easily. It handles localized routes and adds the necessary metadata for search engines.

    To use it, you first need to configure your vite.config.ts to enable pre-rendering for your localized routes and disable the default TanStack Start sitemap generation.

    vite.config.ts

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    import { localeFlatMap } from "intlayer";// ... other importsexport const pathList = ["", "/about", "/404"];const localizedPages = localeFlatMap(({ urlPrefix }) =>  pathList.map((path) => ({    path: `${urlPrefix}${path}`,    prerender: {      enabled: true,    },  })));export default defineConfig({  plugins: [    // ... other plugins    tanstackStart({      // ... other config      sitemap: {        enabled: false,      },      prerender: {        enabled: true,        crawlLinks: false,        concurrency: 10,      },      pages: localizedPages,    }),  ],});

    Then, create a src/routes/sitemap[.]xml.ts route that uses the generateSitemap function:

    src/routes/sitemap[.]xml.ts

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    import { createFileRoute } from "@tanstack/react-router";import { generateSitemap } from "intlayer";const SITE_URL = (  import.meta.env.VITE_SITE_URL ?? "http://localhost:3000").replace(/\/$/, "");export const Route = createFileRoute("/sitemap.xml")({  server: {    handlers: {      GET: async () => {        const sitemap = generateSitemap(          [            { path: "/", changefreq: "daily", priority: 1.0 },            { path: "/about", changefreq: "monthly", priority: 0.8 },          ],          { siteUrl: SITE_URL }        );        return new Response(sitemap, {          headers: { "Content-Type": "application/xml" },        });      },    },  },});

    ---

17. 17

    Configure TypeScript

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

    Ensure your TypeScript configuration includes the autogenerated types:

    tsconfig.json

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    {  // ... 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:

# 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

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.

Go Further

To go further, you can implement the visual editor or externalise your content using the CMS.

Documentation References

• Intlayer Documentation
• Tanstack Start Documentation
• useIntlayer hook
• useLocale hook
• Content Declaration
• Configuration