Translate your Astro + Svelte site with Intlayer | Internationalisation (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 Configure Intlayer in Astro + Svelte

Check out the application template on GitHub.

1. 1

   Install Dependencies

   Install the necessary packages using your preferred package manager:

   bash

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   npm install intlayer astro-intlayer svelte svelte-intlayer @astrojs/sveltenpx 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.

   • svelte Core Svelte package.

   • svelte-intlayer Package to integrate Intlayer into Svelte applications. It provides setupIntlayer as well as the useIntlayer and useLocale stores for internationalisation in Svelte.

   • @astrojs/svelte Official Astro integration that allows the use of Svelte component islands.

2. 2

   Configure Your Project

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

   intlayer.config.ts

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   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.

3. 3

   Integrate Intlayer into Your Astro Configuration

   Add the intlayer plugin and Svelte integration to your Astro configuration.

   astro.config.ts

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

   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 svelte() integration allows for using Svelte component islands via client:only="svelte".

4. 4

   Declare Your Content

   Create and manage your content declarations to store translations:

   src/app.content.ts

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   import { t, type Dictionary } from "intlayer";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.

5. 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 Svelte island for interactive client-side content.

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

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   ---import {  getIntlayer,  getLocaleFromPath,  getLocalizedUrl,  getHTMLTextDir,  getPrefix,  localeMap,  defaultLocale,  type LocalesValues,} from "intlayer";import SvelteIsland from "../../components/svelte/SvelteIsland.svelte";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 Svelte island renders all interactive content, including the language switcher -->    <SvelteIsland locale={locale} client:only="svelte" />  </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.

6. 6

   Create a Svelte Island Component

   Create an island component that wraps your Svelte application. You must call setupIntlayer with the server-detected locale before accessing the stores.

   src/components/svelte/SvelteIsland.svelte

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   <script lang="ts">  import { useIntlayer, useLocale, setupIntlayer } from "svelte-intlayer";  import { getLocalizedUrl, getLocaleName, type LocalesValues } from "intlayer";  export let locale: LocalesValues;  setupIntlayer(locale);  const content = useIntlayer("app");  const { locale: currentLocale, availableLocales, setLocale } = useLocale({    onLocaleChange: (newLocale: LocalesValues) => {      window.location.href = getLocalizedUrl(window.location.pathname, newLocale);    },  });</script><div>  <h1>{$content.title}</h1>  <!-- The language switcher is rendered directly within the island -->  <div class="locale-switcher">    <span class="switcher-label">Change language:</span>    <div class="locale-buttons">      {#each availableLocales as localeItem}        <button          class="locale-btn {localeItem === $currentLocale ? 'active' : ''}"          disabled={localeItem === $currentLocale}          on: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>      {/each}    </div>  </div></div>

   The locale prop is passed from the Astro page (server detection) and used to initialise setupIntlayer, setting the initial language for all stores in the component.

7. 7

   Add a Language Switcher

   The language switching functionality is integrated directly within the Svelte island (see step 6 above). It uses the useLocale store from svelte-intlayer and navigates to the localised URL when a user selects a new language:

   src/components/svelte/SvelteIsland.svelte

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   <script lang="ts">  import { useLocale } from "svelte-intlayer";  import { getLocalizedUrl, getLocaleName, type LocalesValues } from "intlayer";  // Reuse the same locale/setupIntlayer logic from step 6...  const {    locale: currentLocale,    availableLocales,    setLocale,  } = useLocale({    onLocaleChange: (newLocale: LocalesValues) => {      // Navigate to the localised URL on language change      window.location.href = getLocalizedUrl(window.location.pathname, newLocale);    },  });</script><div class="locale-switcher">  <span class="switcher-label">Change language:</span>  <div class="locale-buttons">    {#each availableLocales as localeItem}      <button        class="locale-btn {localeItem === $currentLocale ? 'active' : ''}"        disabled={localeItem === $currentLocale}        on: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>    {/each}  </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.

8. 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.

   src/pages/sitemap.xml.ts

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   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

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   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

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   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

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   npx intlayer extract

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

   vite.config.ts

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

   bash

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   npm run build # Or npm run dev

   ---

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.

Deepen Your Knowledge

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