Translate your Astro + Lit website using Intlayer | Internationalization (i18n)

Table of Contents

Why Intlayer over alternatives?

Compared to main solutions like astro-i18n or i18next, Intlayer is a solution that comes with integrated optimizations such as:

Step-by-Step Guide to Set Up Intlayer in Astro + Lit

See Application Template on GitHub.

1. 1

   Install Dependencies

   Install the necessary packages using your package manager:

   bash

   Copy content

   Copy code

   Copy the code to the clipboard

   npm install intlayer astro-intlayer lit lit-intlayer @astrojs/litnpx intlayer init

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

   • astro-intlayer Includes the Astro integration 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.

   • lit The core Lit package for building fast, lightweight Web Components.

   • lit-intlayer The package that integrates Intlayer with Lit applications. It provides ReactiveController-based hooks (useIntlayer, useLocale, etc.) so that LitElements automatically re-render when the locale changes.

   • @astrojs/lit The official Astro integration that enables Lit custom elements in Astro pages.

2. 2

   Configuration of your project

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

   intlayer.config.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   import { Locales, type IntlayerConfig } from "intlayer";const config: IntlayerConfig = {  internationalization: {    locales: [      Locales.ENGLISH,      Locales.FRENCH,      Locales.SPANISH,      // Your other locales    ],    defaultLocale: Locales.ENGLISH,  },};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.

3. 3

   Integrate Intlayer in Your Astro Configuration

   Add the intlayer plugin and the Lit integration into your configuration.

   astro.config.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   // @ts-checkimport { intlayer } from "astro-intlayer";import lit from "@astrojs/lit";import { defineConfig } from "astro/config";// https://astro.build/configexport default defineConfig({  integrations: [intlayer(), lit()],});

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

   The lit() integration enables Lit custom elements in Astro pages.

4. 4

   Declare Your Content

   Create and manage your content declarations to store translations:

   src/components/lit/app.content.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   import { t, type Dictionary } from "intlayer";const litDemoContent = {  key: "lit-demo",  content: {    greeting: t({      en: "Hello World",      fr: "Bonjour le monde",      es: "Hola mundo",    }),    description: t({      en: "Welcome to my multilingual Astro + Lit site.",      fr: "Bienvenue sur mon site Astro + Lit multilingue.",      es: "Bienvenido a mi sitio Astro + Lit multilingüe.",    }),  },} satisfies Dictionary;export default litDemoContent;

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

   For more details, refer to the content declaration documentation.

5. 5

   Use your content in Astro

   You can consume dictionaries directly in .astro files using the core helpers exported by intlayer. You should also add SEO metadata like hreflang and canonical links to each page. The Lit custom element is then imported via a client-side <script> and placed in the body.

   src/pages/[...locale]/index.astro

   Copy content

   Copy code

   Copy the code to the clipboard

   ---import {  getIntlayer,  getLocaleFromPath,  getLocalizedUrl,  getPrefix,  localeMap,  defaultLocale,  getHTMLTextDir,  type LocalesValues,} from "intlayer";export const getStaticPaths = () => {  return localeMap(({ locale }) => ({    params: { locale: getPrefix(locale).localePrefix },  }));};const locale = getLocaleFromPath(Astro.url.pathname) as LocalesValues;const { greeting } = getIntlayer("lit-demo", locale);---<!doctype html><html lang={locale} dir={getHTMLTextDir(locale)}>  <head>    <meta charset="utf-8" />    <meta name="viewport" content="width=device-width" />    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />    <title>{greeting}</title>    <!-- Canonical link -->    <link      rel="canonical"      href={new URL(getLocalizedUrl(Astro.url.pathname, locale), Astro.site)}    />    <!-- Hreflang links -->    {      localeMap(({ locale: mapLocale }) => (        <link          rel="alternate"          hreflang={mapLocale}          href={new URL(            getLocalizedUrl(Astro.url.pathname, mapLocale),            Astro.site          )}        />      ))    }    <link      rel="alternate"      hreflang="x-default"      href={new URL(        getLocalizedUrl(Astro.url.pathname, defaultLocale),        Astro.site      )}    />  </head>  <body>    <!-- The Lit custom element - receives the server-detected locale as a property -->    <lit-demo locale={locale}></lit-demo>  </body></html><script>  import "../../components/lit/LitDemo";</script>

   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

   Copy content

   Copy code

   Copy the code to the clipboard

   <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)}" />

   Note on Routing Configuration: The directory structure you use depends on the middleware.routing setting in your intlayer.config.ts:

   • prefix-no-default (default): Keeps the default locale at the root (no prefix) and prefixes others. Use [...locale] to catch all cases.
   • prefix-all: All URLs are prefixed with the locale. You can use standard [locale] if you don't need to handle the root separately.
   • search-param or no-prefix: No locale folder is needed. The locale is handled via search parameters or cookies.

6. 6

   Create the Lit custom element

   Create the Lit custom element. installIntlayer is called in connectedCallback with the server-detected locale property to initialize the Intlayer singleton on the client.

   src/components/lit/LitDemo.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   import { LitElement, html } from "lit";import { installIntlayer, useIntlayer, useLocale } from "lit-intlayer";import { getLocalizedUrl, getLocaleName, type LocalesValues } from "intlayer";class LitDemo extends LitElement {  static properties = {    locale: { type: String },  };  locale: LocalesValues = "en" as LocalesValues;  private _content = useIntlayer(this, "lit-demo");  private _localeCtrl = useLocale(this, {    onLocaleChange: (newLocale: LocalesValues) => {      window.location.href = getLocalizedUrl(        window.location.pathname,        newLocale      );    },  });  override connectedCallback() {    super.connectedCallback();    // Initialize with the server-detected locale    installIntlayer({ locale: this.locale as any });  }  override render() {    const { greeting, description } = this._content;    const {      locale: currentLocale,      availableLocales,      setLocale,    } = this._localeCtrl;    return html`      <div>        <h1>${greeting}</h1>        <p>${description}</p>        <!-- Locale switcher is rendered inline in the LitElement -->        <div class="locale-switcher">          <span class="switcher-label">Switch locale:</span>          <div class="locale-buttons">            ${availableLocales.map(              (localeItem) => html`                <button                  class="locale-btn ${localeItem === currentLocale                    ? "active"                    : ""}"                  ?disabled=${localeItem === currentLocale}                  @click=${() => setLocale(localeItem)}                >                  <span class="ls-own-name">${getLocaleName(localeItem)}</span>                  <span class="ls-current-name"                    >${getLocaleName(localeItem, currentLocale)}</span                  >                  <span class="ls-code">${localeItem.toUpperCase()}</span>                </button>              `            )}          </div>        </div>      </div>    `;  }}customElements.define("lit-demo", LitDemo);

   The locale property is passed from the Astro page (server-detected) and used in connectedCallback to initialise installIntlayer, making it the initial locale for all ReactiveController hooks in the element.

   useIntlayer registers itself as a ReactiveController. The element re-renders automatically when the locale changes - no extra setup required.

7. 7

   Add a Locale Switcher

   The locale switcher is embedded directly in the Lit custom element's render() method (shown in Step 6). It uses useLocale from lit-intlayer and navigates to the localized URL when the user picks a new language:

   src/components/lit/LitDemo.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   // Within the LitElement class, after useLocale setup (shown in Step 6):private _localeCtrl = useLocale(this, {  onLocaleChange: (newLocale: LocalesValues) => {    // Navigate to the localized URL on locale change    window.location.href = getLocalizedUrl(window.location.pathname, newLocale);  },});override render() {  const { locale: currentLocale, availableLocales, setLocale } = this._localeCtrl;  return html`    <div class="locale-switcher">      <span class="switcher-label">Switch locale:</span>      <div class="locale-buttons">        ${availableLocales.map(          (localeItem) => html`            <button              class="locale-btn ${localeItem === currentLocale ? "active" : ""}"              ?disabled=${localeItem === currentLocale}              @click=${() => setLocale(localeItem)}            >              <span class="ls-own-name">${getLocaleName(localeItem)}</span>              <span class="ls-current-name">${getLocaleName(localeItem, currentLocale)}</span>              <span class="ls-code">${localeItem.toUpperCase()}</span>            </button>          `        )}      </div>    </div>  `;}

   Note on Lit Reactivity: useLocale returns a ReactiveController. When setLocale is called, the controller schedules a re-render automatically - so the active button state updates without manual DOM manipulation.

   Note on Persistence: Using onLocaleChange to redirect via window.location.href ensures that the new locale URL is visited, allowing Intlayer middleware to set the locale cookie and remember the user's preference on future visits.

8. 8

   Sitemap and Robots.txt

   Intlayer provides utilities to generate localized sitemaps and robots.txt files dynamically.

   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.

   The Intlayer generated sitemap supports the xhtml:link namespace (Hreflang XML Extensions). Unlike the default sitemap generators that only list raw URLs, Intlayer automatically creates the required bidirectional links between all language versions of a page (e.g., /about, /about?lang=fr, and /about?lang=es). This ensures search engines correctly index and serve the right language version to the right audience.

   Create src/pages/sitemap.xml.ts to generate a sitemap that includes all your localized routes.

   src/pages/sitemap.xml.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   import type { APIRoute } from "astro";import { generateSitemap, type SitemapUrlEntry } from "intlayer";const pathList: SitemapUrlEntry[] = [  { path: "/", changefreq: "daily", priority: 1.0 },  { path: "/about", changefreq: "monthly", priority: 0.7 },];const SITE_URL = import.meta.env.SITE ?? "http://localhost:4321";export const GET: APIRoute = async ({ site }) => {  const xmlOutput = generateSitemap(pathList, { siteUrl: SITE_URL });  return new Response(xmlOutput, {    headers: { "Content-Type": "application/xml" },  });};

   Robots.txt

   Create src/pages/robots.txt.ts to control search engine crawling.

   src/pages/robots.txt.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   import type { APIRoute } from "astro";import { getMultilingualUrls } from "intlayer";const getAllMultilingualUrls = (urls: string[]) =>  urls.flatMap((url) => Object.values(getMultilingualUrls(url)) as string[]);const disallowedPaths = getAllMultilingualUrls(["/admin", "/private"]);export const GET: APIRoute = ({ site }) => {  const robotsTxt = [    "User-agent: *",    "Allow: /",    ...disallowedPaths.map((path) => `Disallow: ${path}`),    "",    `Sitemap: ${new URL("/sitemap.xml", site).href}`,  ].join("\n");  return new Response(robotsTxt, {    headers: { "Content-Type": "text/plain" },  });};

9. 15

   Extract the content of your components

   Optional

   If you have an existing codebase, transforming thousands of files can be time-consuming.

   To ease this process, Intlayer propose a compiler / extractor to transform your components and extract the content.

   To set it up, you can add a compiler section in your intlayer.config.ts file:

   intlayer.config.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   import { type IntlayerConfig } from "intlayer";
   
   const config: IntlayerConfig = {
     // ... Rest of your config
     compiler: {
       /**
        * Indicates if the compiler should be enabled.
        */
       enabled: true,
   
       /**
        * Defines the output files path
        */
       output: ({ fileName, extension }) => `./${fileName}${extension}`,
   
       /**
        * Indicates if the components should be saved after being transformed.
        *
        * - If `true`, the compiler will rewrite the component file in the disk. So the transformation will be permanent, and the compiler will skip the transformation for the next process. That way, the compiler can transform the app, and then it can be removed.
        *
        * - If `false`, the compiler will inject the `useIntlayer()` function call into the code in the build output only, and keep the base codebase intact. The transformation will be done only in memory.
        */
       saveComponents: false,
   
       /**
        * Dictionary key prefix
        */
       dictionaryKeyPrefix: "",
     },
   };
   
   export default config;

   Extract commandBabel compiler

   Run the extractor to transform your components and extract the content

   bash

   Copy content

   Copy code

   Copy the code to the clipboard

   npx intlayer extract

   Update your vite.config.ts to include the intlayerCompiler plugin:

   vite.config.ts

   Copy content

   Copy code

   Copy the code to the clipboard

   import { defineConfig } from "vite";import { intlayer, intlayerCompiler } from "vite-intlayer";export default defineConfig({ plugins: [   intlayer(),   intlayerCompiler(), // Adds the compiler plugin ],});

   bash

   Copy content

   Copy code

   Copy the code to the clipboard

   npm run build # Or npm run dev

   ---

Configure TypeScript

Intlayer use module augmentation to get benefits of TypeScript and make your codebase stronger. Lit requires experimentalDecorators to be enabled if you use the decorator syntax.

Ensure your TypeScript configuration includes the autogenerated types.

{  compilerOptions: {    // ...    experimentalDecorators: true,    useDefineForClassFields: false, // Required by Lit for decorator support  },  include: [    // ... Your existing TypeScript configurations    ".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 externalize your content using the CMS.