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    Creation:2025-09-09Last update:2025-11-18

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

    Table of Contents

    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

    See Application Template on GitHub.

    Step 1: Create Project

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

    Step 2: Install Intlayer Packages

    Install the necessary packages using your preferred package manager:

    npm install intlayer react-intlayernpm install vite-intlayer --save-dev
    • intlayer

      The core package that provides internationalization 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 internationalization.

    • 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.

    Step 3: Configuration of your project

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

    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.

    Step 4: Integrate Intlayer in Your Vite Configuration

    Add the intlayer plugin into your configuration:

    vite.config.ts
    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";import viteTsConfigPaths from "vite-tsconfig-paths";const config = defineConfig({  plugins: [    nitro(),    viteTsConfigPaths({      projects: ["./tsconfig.json"],    }),    tanstackStart(),    viteReact(),    intlayer(), // To add  ],});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 optimize performance.

    Step 5: Create Layout Components

    Set up your root layout and locale-specific layouts:

    Root Layout

    src/routes/{-$locale}/route.tsx
    import { createFileRoute, Outlet } from "@tanstack/react-router";import { IntlayerProvider, useLocale } from "react-intlayer";import { useI18nHTMLAttributes } from "@/hooks/useI18nHTMLAttributes";export const Route = createFileRoute("/{-$locale}")({  component: LayoutComponent,});function LayoutComponent() {  const { defaultLocale } = useLocale();  const { locale } = Route.useParams();  return (    <IntlayerProvider locale={locale ?? defaultLocale}>      <Outlet />    </IntlayerProvider>  );}
    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.

    Step 6: Declare Your Content

    Create and manage your content declarations to store translations:

    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.

    Step 7: Create Locale-Aware Components and Hooks

    Create a LocalizedLink component for locale-aware navigation:

    src/components/localized-link.tsx
    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 = "{-$locale}" as const;// Main utilityexport type RemoveLocaleParam<T> = T extends string  ? RemoveLocaleFromString<T>  : T;export type To = RemoveLocaleParam<LinkComponentProps["to"]>;type CollapseDoubleSlashes<S extends string> =  S extends `${infer H}//${infer T}` ? CollapseDoubleSlashes<`${H}/${T}`> : S;type LocalizedLinkProps = {  to?: To;} & Omit<LinkComponentProps, "to">;// Helperstype RemoveAll<  S extends string,  Sub extends string,> = S extends `${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();  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 localized route.

    Then we can create a useLocalizedNavigate hook for programmatic navigation:

    src/hooks/useLocalizedNavigate.tsx
    import { useNavigate } from "@tanstack/react-router";import { getPrefix } from "intlayer";import { useLocale } from "react-intlayer";import { LOCALE_ROUTE } from "@/components/localized-link";import type { FileRouteTypes } from "@/routeTree.gen";type StripLocalePrefix<T extends string> = T extends  | `/${typeof LOCALE_ROUTE}`  | `/${typeof LOCALE_ROUTE}/`  ? "/"  : T extends `/${typeof LOCALE_ROUTE}/${infer Rest}`    ? `/${Rest}`    : never;type LocalizedTo = StripLocalePrefix<FileRouteTypes["to"]>;type LocalizedNavigate = {  (to: LocalizedTo): ReturnType<ReturnType<typeof useNavigate>>;  (    opts: { to: LocalizedTo } & Record<string, unknown>  ): ReturnType<ReturnType<typeof useNavigate>>;};export const useLocalizedNavigate = () => {  const navigate = useNavigate();  const { locale } = useLocale();  const localizedNavigate: LocalizedNavigate = (args: any) => {    const { localePrefix } = getPrefix(locale);    if (typeof args === "string") {      return navigate({        to: `/${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;};

    Step 8: Utilize Intlayer in Your Pages

    Access your content dictionaries throughout your application:

    Localized Home Page

    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.

    Step 9: Create a Locale Switcher Component

    Create a component to allow users to change languages:

    src/components/locale-switcher.tsx
    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 { LocalizedLink, 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}>          <LocalizedLink            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>          </LocalizedLink>        </li>      ))}    </ol>  );};
    To Learn more about the useLocale hook, refer to the documentation.

    Step 10: Add HTML Attributes Management (Optional)

    Create a hook to manage HTML lang and dir attributes:

    src/hooks/useI18nHTMLAttributes.tsx
    // src/hooks/useI18nHTMLAttributes.tsximport { 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:

    src/routes/{-$locale}/index.tsx
    import { createFileRoute, Outlet } from "@tanstack/react-router";import { IntlayerProvider } from "react-intlayer";import { useI18nHTMLAttributes } from "@/hooks/useI18nHTMLAttributes"; // import the hookexport const Route = createFileRoute("/{-$locale}")({  component: LayoutComponent,});function LayoutComponent() {  useI18nHTMLAttributes(); // add this line  const { locale } = Route.useParams();  return (    <IntlayerProvider      locale={locale} // If no locale included as a parameter, the default locale will be used    >      <Outlet />    </IntlayerProvider>  );}

    Step 11: Add middleware (Optional)

    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
    import { reactRouter } from "@react-router/dev/vite";import tailwindcss from "@tailwindcss/vite";import { defineConfig } from "vite";import { intlayer, intlayerProxy } from "vite-intlayer";import tsconfigPaths from "vite-tsconfig-paths";export default defineConfig({  plugins: [    intlayerProxy(), // The proxy should be placed before server if you use Nitro    tailwindcss(),    reactRouter(),    tsconfigPaths(),    intlayer(),  ],});

    Step 12: Internationalize your Metadata (Optional)

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

    src/routes/{-$locale}/index.tsx
    import { createFileRoute } from "@tanstack/react-router";import { getIntlayer } from "intlayer";export const Route = createFileRoute("/{-$locale}/")({  component: RouteComponent,  head: ({ params }) => {    const { locale } = params;    const metaContent = getIntlayer("page-metadata", locale);    return {      meta: [        { title: metaContent.title },        { content: metaContent.description, name: "description" },      ],    };  },});

    Step 13: Retrieve the locale in your server actions (Optional)

    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
    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')    getHeader: (name) => getRequestHeader(name),    // Fallback using Accept-Language negotiation    getAllHeaders: async () => {      const headers = getRequestHeaders();      const result: Record<string, string> = {};      // Convert the TypedHeaders into a plain Record<string, string>      for (const [key, value] of headers.entries()) {        result[key] = value;      }      return result;    },  });  // Retrieve some content using getIntlayer()  const content = getIntlayer("app", locale);  return { locale, content };});

    Step 14: 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:

    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:

    .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

    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 externalize your content using the CMS.


    Documentation References

    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.

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