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

Table of Contents

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.

Step-by-Step Guide to Set Up Intlayer in Astro + Vanilla JS

See Application Template on GitHub.

Step 1: Install Dependencies

Install the necessary packages using your package manager:

npm install intlayer astro-intlayer vanilla-intlayernpx 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.

• vanilla-intlayer The package that integrates Intlayer with plain JavaScript / TypeScript applications. It provides a pub/sub singleton (IntlayerClient) and callback-based helpers (useIntlayer, useLocale, etc.) so any part of your Astro <script> blocks can react to locale changes without a UI framework.

Step 2: Configuration of your project

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

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.

Step 3: Integrate Intlayer in Your Astro Configuration

Add the intlayer plugin into your configuration. No extra UI-framework integration is needed for Vanilla JS.

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

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.

Step 4: Declare Your Content

Create and manage your content declarations to store translations:

import { t, type Dictionary } from "intlayer";const appContent = {  key: "app",  content: {    greeting: t({      en: "Hello World",      fr: "Bonjour le monde",      es: "Hola mundo",    }),    description: t({      en: "Welcome to my multilingual Astro site.",      fr: "Bienvenue sur mon site Astro multilingue.",      es: "Bienvenido a mi sitio Astro multilingüe.",    }),    switchLocale: t({      en: "Switch language:",      fr: "Changer de langue :",      es: "Cambiar idioma:",    }),  },} 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, ./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.

Step 5: Use your content in Astro

With Vanilla JS, all rendering is done directly in the .astro file using getIntlayer for the initial server render. A <script> block then bootstraps vanilla-intlayer on the client side for locale switching.

---import {  getIntlayer,  getLocaleFromPath,  getLocalizedUrl,  getPrefix,  getLocaleName,  localeMap,  locales,  defaultLocale,  getPathWithoutLocale,  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 pathWithoutLocale = getPathWithoutLocale(Astro.url.pathname);const { greeting, description, switchLocale } = getIntlayer("app", 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>    <main>      <h1 id="greeting">{greeting}</h1>      <p id="description">{description}</p>      <div class="locale-switcher">        <span class="switcher-label">{switchLocale}</span>        <div class="locale-buttons">          {            locales.map((localeItem) => (              <a                href={localeItem === locale ? undefined : getLocalizedUrl(pathWithoutLocale, localeItem)}                class={`locale-btn ${localeItem === locale ? "active" : ""}`}                data-locale={localeItem}                aria-disabled={localeItem === locale}              >                {getLocaleName(localeItem)}              </a>            ))          }        </div>      </div>    </main>  </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)}" />

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.

Step 6: Add a Locale Switcher

With Vanilla JS in Astro, the locale switcher is rendered server-side as anchor links and hydrated on the client via a <script> block. When the user clicks a locale link, vanilla-intlayer sets the locale cookie via setLocale before navigating to the localized URL.

<!-- server-side markup shown in Step 5 above --><script>  import { installIntlayer, useLocale } from "vanilla-intlayer";  import { getLocaleFromPath, getLocalizedUrl, type LocalesValues } from "intlayer";  // Bootstrap Intlayer on the client using the current URL's locale  const locale = getLocaleFromPath(window.location.pathname);  installIntlayer({ locale: locale as LocalesValues });  const { setLocale } = useLocale({    onLocaleChange: (newLocale: LocalesValues) => {      window.location.href = getLocalizedUrl(window.location.pathname, newLocale);    },  });  // Attach click handlers to locale anchor links  const localeLinks = document.querySelectorAll("[data-locale]");  localeLinks.forEach((link) => {    link.addEventListener("click", (e) => {      const localeValue = link.getAttribute("data-locale") as LocalesValues;      if (localeValue && localeValue !== locale) {        e.preventDefault();        setLocale(localeValue);      }    });  });</script>

Note on Persistence: installIntlayer bootstraps the Intlayer singleton with the server-detected locale. useLocale with onLocaleChange then sets the locale cookie via the middleware before navigating, so the user's preference is remembered on future visits.

Note on Progressive Enhancement: The locale links work as standard <a> tags even without JavaScript. When JS is available, the setLocale call updates the cookie before the navigation so the middleware can redirect correctly.

Step 7: 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.

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.

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" },  });};

Configure TypeScript

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

Ensure your TypeScript configuration includes the autogenerated types.

{  // ... Your existing TypeScript configurations  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.

(Optional) Step 15: Extract the content of your components

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:

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;

npx intlayer extract

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

npm run build # Or npm run dev

Go Further

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