Translate your Astro + Vanilla JS site with Intlayer | Internationalisation (i18n)

Table of Contents

What is Intlayer?

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

With Intlayer, you can:

• Manage translations easily: Using declarative dictionaries at the component level.
• Localise metadata, routes and content dynamically.
• Ensure TypeScript support: With autogenerated types for better autocompletion and error detection.
• Benefit from advanced features: Such as dynamic language detection and switching.

Step-by-Step Guide to Configure Intlayer in Astro + Vanilla JS

Check out the application template on GitHub.

Step 1: Install Dependencies

Install the necessary packages using your preferred package manager:

npm install intlayer astro-intlayer vanilla-intlayernpx intlayer init

• intlayer The core package that provides i18n tools for configuration management, translations, content declaration, transpilation, and CLI commands.

• astro-intlayer Includes the Astro integration plugin to link Intlayer with the Vite bundler, as well as the middleware to detect the user's preferred language, manage cookies, and handle URL redirects.

• vanilla-intlayer A package to integrate Intlayer into Vanilla JavaScript / TypeScript applications. It provides a Pub/Sub singleton (IntlayerClient) and callback-based helpers (useIntlayer, useLocale, etc.), allowing any part of your Astro <script> tags to respond to language changes without the need for a UI framework.

Step 2: Configure Your Project

Create a configuration file to define your application's languages:

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

Through this configuration file, you can configure localised URLs, middleware redirects, cookie names, location and extensions of content declarations, disable Intlayer logs in the console, and more. For a full list of available parameters, refer to the configuration documentation.

Step 3: Integrate Intlayer into Your Astro Configuration

Add the intlayer plugin to your Astro configuration. For Vanilla JS, no additional UI framework integration is required.

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

The intlayer() integration plugin is used to integrate Intlayer with Astro. It ensures the generation of the content declaration files and monitors them in development mode. It defines Intlayer environment variables within the Astro application and provides aliases to optimise 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",      "en-GB": "Hello World",    }),    description: t({      en: "Welcome to my multilingual Astro site.",      fr: "Bienvenue sur mon site Astro multilingue.",      es: "Bienvenido a mi sitio Astro multilingüe.",      "en-GB": "Welcome to my multilingual Astro site.",    }),    switchLocale: t({      en: "Switch language:",      fr: "Changer de langue :",      es: "Cambiar idioma:",      "en-GB": "Change language:",    }),  },} satisfies Dictionary;export default appContent;

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

For more information, refer to the content declaration documentation.

Step 5: Using Content in Astro

With Vanilla JS, all server-side rendering happens directly in .astro files using getIntlayer. Subsequently, a <script> block initialises vanilla-intlayer on the client to enable language switching.

---import {  getIntlayer,  getLocaleFromPath,  getLocalizedUrl,  getPrefix,  getLocaleName,  localeMap,  locales,  defaultLocale,  getPathWithoutLocale,  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 setup: The directory structure you use depends on the middleware.routing setting in intlayer.config.ts:

• prefix-no-default (default): keeps the default language at the root (no prefix) and prefixes others. Use [...locale] to catch all cases.
• prefix-all: all URLs get a language prefix. You can use standard [locale] if you don't need to handle the root separately.
• search-param or no-prefix: no language directories are needed. The language is handled via query parameters or cookies.

Step 6: Adding a Language Switcher

In Astro with Vanilla JS, the language switcher is rendered on the server as regular links and hydrated on the client via a <script> block. When a user clicks a language link, vanilla-intlayer sets the language cookie via setLocale before navigating to the localised URL.

<!-- Include the server-side markup from step 5 above --><script>  import { installIntlayer, useLocale } from "vanilla-intlayer";  import { getLocaleFromPath, getLocalizedUrl, type LocalesValues } from "intlayer";  // Initialise Intlayer on the client with the locale taken from the current path  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);    },  });  // Bind click events to language switcher 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 initialises the Intlayer singleton with the server-defined locale. useLocale with onLocaleChange ensures the language cookie is set before navigating via the middleware, so that the user's language preference is remembered in future visits.

Note on Progressive Enhancement: The links in the language switcher will work as standard <a> tags even without JavaScript. When JavaScript is available, calls to setLocale will update the cookie before navigating, ensuring the middleware performs the correct redirect.

Step 7: Sitemap and Robots.txt

Intlayer offers utilities to dynamically create your localised sitemap and robots.txt files.

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 including all your localised 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" },  });};

TypeScript Configuration

Intlayer uses module augmentation to leverage TypeScript, making your codebase more robust.

Ensure your TypeScript configuration includes the autogenerated types.

{  // ... your existing TypeScript configuration  "include": [    // ... your existing TypeScript configuration    ".intlayer/**/*.ts", // Include autogenerated types  ],}

Git Configuration

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

To do this, 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.

Installation from the VS Code Marketplace

This extension provides:

• Autocompletion for translation keys.
• Real-time error detection for missing translations.
• Inline preview of translated content.
• Quick actions for easily creating and updating translations.

For more information on using the extension, refer to the 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

Deepen Your Knowledge

If you want to learn more, you can also implement the Visual Editor or use the CMS to externalise your content.