Translate your Astro + Preact 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 + Preact

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 preact preact-intlayer @astrojs/preactnpx 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.

• preact Core Preact package - a fast, lightweight alternative to React.

• preact-intlayer Package to integrate Intlayer into Preact applications. It provides the IntlayerProvider as well as the useIntlayer and useLocale hooks for internationalisation in Preact.

• @astrojs/preact Official Astro integration that allows the use of Preact component islands.

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 and Preact integration to your Astro configuration.

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

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.

The preact() integration allows for using Preact component islands via client:only="preact".

Step 4: Declare Your Content

Create and manage your content declarations to store translations:

import { h } from "preact";import { t, type Dictionary } from "intlayer";import type { ComponentChildren } from "preact";const appContent = {  key: "app",  content: {    title: t({      en: "Hello World",      fr: "Bonjour le monde",      es: "Hola mundo",      "en-GB": "Hello World",    }),  },} 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.

If your content files include TSX code, you might need to import import { h } from "preact"; or ensure your JSX pragma is correctly configured for Preact.

Step 5: Using Content in Astro

You can consume the dictionaries directly in your .astro files using the core helpers exported from intlayer. You should also add SEO metadata (such as hreflang and canonical links) to every page and introduce a Preact island for interactive client-side content.

---import {  getIntlayer,  getLocaleFromPath,  getLocalizedUrl,  getHTMLTextDir,  getPrefix,  localeMap,  defaultLocale,  type LocalesValues,} from "intlayer";import { PreactIsland } from "../../components/preact/ReactIsland";export const getStaticPaths = () => {  return localeMap(({ locale }) => ({    params: { locale: getPrefix(locale).localePrefix },  }));};const locale = getLocaleFromPath(Astro.url.pathname) as LocalesValues;const { title } = 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>{title}</title>    <!-- Canonical Link: Informs search engines about the main version of this page -->    <link      rel="canonical"      href={new URL(getLocalizedUrl(Astro.url.pathname, locale), Astro.site)}    />    <!-- Hreflang: Informs Google about all localised versions -->    {      localeMap(({ locale: mapLocale }) => (        <link          rel="alternate"          hreflang={mapLocale}          href={new URL(            getLocalizedUrl(Astro.url.pathname, mapLocale),            Astro.site          )}        />      ))    }    <!-- x-default: Fallback option when locale doesn't match user's language -->    <link      rel="alternate"      hreflang="x-default"      href={new URL(        getLocalizedUrl(Astro.url.pathname, defaultLocale),        Astro.site      )}    />  </head>  <body>    <!-- The Preact island renders all interactive content, including the language switcher -->    <PreactIsland locale={locale} client:only="preact" />  </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: Create a Preact Island Component

Create an island component that wraps your Preact application and receives the server-detected locale:

/** @jsxImportSource preact */import { IntlayerProvider, useIntlayer } from "preact-intlayer";import { type LocalesValues } from "intlayer";import type { FunctionalComponent } from "preact";import { LocaleSwitcher } from "./LocaleSwitcher";const App: FunctionalComponent = () => {  const { title } = useIntlayer("app");  return (    <div>      <h1>{title}</h1>      <LocaleSwitcher />    </div>  );};export const PreactIsland: FunctionalComponent<{ locale: LocalesValues }> = ({  locale,}) => (  <IntlayerProvider locale={locale}>    <App />  </IntlayerProvider>);

The locale prop is passed from the Astro page (server detection) to IntlayerProvider, making it the initial language for all Preact hooks within the tree.

Note: In Preact, the HTML class property is used instead of className.

Step 7: Add a Language Switcher

Create a Preact LocaleSwitcher component that reads available languages and navigates to the localised URL when a user selects a new language:

/** @jsxImportSource preact */import { useLocale } from "preact-intlayer";import { getLocalizedUrl, getLocaleName, type LocalesValues } from "intlayer";import type { FunctionalComponent } from "preact";export const LocaleSwitcher: FunctionalComponent = () => {  const { locale, availableLocales, setLocale } = useLocale({    onLocaleChange: (newLocale: LocalesValues) => {      // Navigate to the localised URL on language change      window.location.href = getLocalizedUrl(        window.location.pathname,        newLocale      );    },  });  return (    <div class="locale-switcher">      <span class="switcher-label">Change language:</span>      <div class="locale-buttons">        {availableLocales.map((localeItem) => (          <button            key={localeItem}            onClick={() => setLocale(localeItem)}            class={`locale-btn ${localeItem === locale ? "active" : ""}`}            disabled={localeItem === locale}          >            <span class="ls-own-name">{getLocaleName(localeItem)}</span>            <span class="ls-current-name">              {getLocaleName(localeItem, locale)}            </span>            <span class="ls-code">{localeItem.toUpperCase()}</span>          </button>        ))}      </div>    </div>  );};

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

The LocaleSwitcher must be rendered within IntlayerProvider - use it in your island component (as shown in step 6).

Step 8: 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 and is configured for Preact:

{  compilerOptions: {    // ...    jsx: "react-jsx",    jsxImportSource: "preact", // Recommended for Preact 10+  },  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

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