Translate your SvelteKit 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. It works seamlessly with SvelteKit's Server-Side Rendering (SSR) capabilities.

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.
• Leverage SvelteKit's SSR for SEO-friendly internationalization.

Step-by-Step Guide to Set Up Intlayer in a SvelteKit Application

See Application Template on GitHub.

To get started, create a new SvelteKit project. Here is the final structure that we will make:

.├── intlayer.config.ts├── package.json├── src│   ├── app.d.ts│   ├── app.html│   ├── hooks.server.ts│   ├── lib│   │   ├── getLocale.ts│   │   ├── LocaleSwitcher.svelte│   │   └── LocalizedLink.svelte│   ├── params│   │   └── locale.ts│   └── routes│       ├── [[locale=locale]]│       │   ├── +layout.svelte│       │   ├── +layout.ts│       │   ├── +page.svelte│       │   ├── +page.ts│       │   ├── about│       │   │   ├── +page.svelte│       │   │   ├── +page.ts│       │   │   └── page.content.ts│       │   ├── Counter.content.ts│       │   ├── Counter.svelte│       │   ├── Header.content.ts│       │   ├── Header.svelte│       │   ├── home.content.ts│       │   └── layout.content.ts│       ├── +layout.svelte│       └── layout.css├── static│   ├── favicon.svg│   └── robots.txt├── svelte.config.js├── tsconfig.json└── vite.config.ts

Step 1: Install Dependencies

Install the necessary packages using npm:

npm install intlayer svelte-intlayernpm install vite-intlayer --save-dev

• intlayer: The core i18n package.
• svelte-intlayer: Provides context providers and stores for Svelte/SvelteKit.
• vite-intlayer: The Vite plugin to integrate content declarations with the build process.

Step 2: Configuration of your project

Create a config file in your project root:

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

Step 3: Integrate Intlayer in Your Vite Configuration

Update your vite.config.ts to include the Intlayer plugin. This plugin handles the transpilation of your content files.

import { sveltekit } from "@sveltejs/kit/vite";import { defineConfig } from "vite";import { intlayer } from "vite-intlayer";export default defineConfig({  plugins: [intlayer(), sveltekit()], // order matters, Intlayer should be placed before SvelteKit});

Step 4: Declare Your Content

Create your content declaration files anywhere in your src folder (e.g., src/lib/content or alongside your components). These files define the translatable content for your application using the t() function for each locale.

import { t, type Dictionary } from "intlayer";const heroContent = {  key: "hero-section",  content: {    title: t({      en: "Welcome to SvelteKit",      fr: "Bienvenue sur SvelteKit",      es: "Bienvenido a SvelteKit",    }),  },} satisfies Dictionary;export default heroContent;

Step 5: Utilize Intlayer in Your Components

Now you can use the useIntlayer function in any Svelte component. It returns a reactive store that automatically updates when the locale changes. The function will automatically respect the current locale (both during SSR and client-side navigation).

Note: useIntlayer returns a Svelte store, so you need to use the $ prefix to access its reactive value (e.g., $content.title).

<script lang="ts">  import { useIntlayer } from "svelte-intlayer";  // "hero-section" corresponds to the key defined in Step 4  const content = useIntlayer("hero-section");</script><!-- Render content as simple content  --><h1>{$content.title}</h1><!-- To render the content editable using the editor --><h1><svelte:component this={$content.title} /></h1><!-- To render the content as a string --><div aria-label={$content.title.value}></div>

(Optional) Step 6: Set up routing

The following steps show how to set up locale-based routing in SvelteKit. This allows your URLs to include the locale prefix (e.g., /en/about, /fr/about) for better SEO and user experience.

.└─── src    ├── app.d.ts                  # Define the locale type    ├── hooks.server.ts           # Manage locale routing    ├── lib    │   └── getLocale.ts          # Check the locale from the header, cookies    ├── params    │   └── locale.ts             # Define the locale parameter    └── routes        ├── [[locale=locale]]     # Wrap in a route group to set the locale        │   ├── +layout.svelte    # Local layout for the route        │   ├── +layout.ts        │   ├── +page.svelte        │   ├── +page.ts        │   └── about        │       ├── +page.svelte        │       └── +page.ts        └── +layout.svelte         # Root layout for fonts and global styles

Step 7: Handle Server-Side Locale Detection (Hooks)

In SvelteKit, the server needs to know the user's locale to render the correct content during SSR. We use hooks.server.ts to detect the locale from the URL or cookies.

Create or modify src/hooks.server.ts:

import type { Handle } from "@sveltejs/kit";import { getLocalizedUrl } from "intlayer";import { getLocale } from "$lib/getLocale";export const handle: Handle = async ({ event, resolve }) => {  const detectedLocale = getLocale(event);  // Check if the current path already starts with a locale (e.g. /fr, /en)  const pathname = event.url.pathname;  const targetPathname = getLocalizedUrl(pathname, detectedLocale);  // If NO locale is present in the URL (e.g. user visits "/"), redirect them  if (targetPathname !== pathname) {    return new Response(undefined, {      headers: { Location: targetPathname },      status: 307, // Temporary redirect    });  }  return resolve(event, {    transformPageChunk: ({ html }) => html.replace("%lang%", detectedLocale),  });};

Then, create a helper to get the user's locale from the request event:

import {  configuration,  getLocaleFromStorage,  localeDetector,  type Locale,} from "intlayer";import type { RequestEvent } from "@sveltejs/kit";/** * Get the user's locale from the request event. * This function is used in the `handle` hook in `src/hooks.server.ts`. * * It first tries to get the locale from the Intlayer storage (cookies or custom headers). * If the locale is not found, it falls back to the browser's "Accept-Language" negotiation. * * @param event - The request event from SvelteKit * @returns The user's locale */export const getLocale = (event: RequestEvent): Locale => {  const defaultLocale = configuration?.internationalization?.defaultLocale;  // Try to get locale from Intlayer storage (Cookies or headers)  const storedLocale = getLocaleFromStorage({    // SvelteKit cookies access    getCookie: (name: string) => event.cookies.get(name) ?? null,    // SvelteKit headers access    getHeader: (name: string) => event.request.headers.get(name) ?? null,  });  if (storedLocale) {    return storedLocale;  }  // Fallback to Browser "Accept-Language" negotiation  const negotiatorHeaders: Record<string, string> = {};  // Convert SvelteKit Headers object to a plain Record<string, string>  event.request.headers.forEach((value, key) => {    negotiatorHeaders[key] = value;  });  // Check the locale from the `Accept-Language` header  const userFallbackLocale = localeDetector(negotiatorHeaders);  if (userFallbackLocale) {    return userFallbackLocale;  }  // Return default locale if no match is found  return defaultLocale;};

getLocaleFromStorage will check the locale from header or cookie depending on your configuration. See Configuration for more details.

The localeDetector function will treat the Accept-Language header and return the best match.

If the locale is not configured, we want to return a 404 error. To make it easier, we can create a match function to check if the locale is valid:

import { configuration, type Locale } from "intlayer";export const match = (  param: Locale = configuration.internationalization.defaultLocale): boolean => {  return configuration.internationalization.locales.includes(param);};

Note: Ensure your src/app.d.ts includes the locale definition:

declare global {  namespace App {    interface Locals {      locale: import("intlayer").Locale;    }  }}

For the +layout.svelte file, we can remove everything, to keep only static content, not related to i18n:

<script lang="ts">     import './layout.css';    let { children } = $props();</script><div class="app">    {@render children()}</div><style>    .app {    /*  */    }</style>

Then, create a new page and layout under the [[locale=locale]] group:

import type { Load } from "@sveltejs/kit";import { configuration, type Locale } from "intlayer";export const prerender = true;// Use the generic Load typeexport const load: Load = ({ params }) => {  const locale: Locale =    (params.locale as Locale) ??    configuration.internationalization.defaultLocale;  return {    locale,  };};

<script lang="ts">    import type { Snippet } from 'svelte';    import { useIntlayer, setupIntlayer } from 'svelte-intlayer';    import Header from './Header.svelte';    import type { LayoutData } from './$types';    let { children, data }: { children: Snippet, data: LayoutData } = $props();    // Initialize Intlayer with the locale from the route    setupIntlayer(data.locale);    // Use the layout content dictionary    const layoutContent = useIntlayer('layout');</script><Header /><main>    {@render children()}</main><footer>    <p>        {$layoutContent.footer.prefix.value}{' '}        <a href="https://svelte.dev/docs/kit">{$layoutContent.footer.linkLabel.value}</a>{' '}        {$layoutContent.footer.suffix.value}    </p></footer><style>  /*  */</style>

export const prerender = true;

<script lang="ts">    import { useIntlayer } from 'svelte-intlayer';    // Use the home content dictionary    const homeContent = useIntlayer('home');</script><svelte:head>    <title>{$homeContent.title.value}</title></svelte:head><section>    <h1>        {$homeContent.title}    </h1></section><style>  /*  */</style>

(Optional) Step 8: Internationalized Links

For SEO, it is recommended to prefix your routes with the locale (e.g., /en/about, /fr/about). This component automatically prefixes any link with the current locale.

<script lang="ts">  import { getLocalizedUrl } from "intlayer";  import { useLocale } from 'svelte-intlayer';  let { href = "" } = $props();  const { locale } = useLocale();  // Helper to prefix URL with current locale  $: localizedHref = getLocalizedUrl(href, $locale);</script><a href={localizedHref}>  <slot /></a>

If you use goto from SvelteKit, you can use the same logic with getLocalizedUrl to navigate to the localized URL:

import { goto } from "$app/navigation";import { getLocalizedUrl } from "intlayer";import { useLocale } from "svelte-intlayer";const { locale } = useLocale();const localizedPath = getLocalizedUrl("/about", $locale);goto(localizedPath); // Navigates to /en/about or /fr/about depending on locale

(Optional) Step 9: Language Switcher

To allow users to switch languages, update the URL.

<script lang="ts">  import { getLocalizedUrl, getLocaleName } from 'intlayer';  import { useLocale } from 'svelte-intlayer';  import { page } from '$app/stores';  import { goto } from '$app/navigation';  const { locale, setLocale, availableLocales } = useLocale({    onLocaleChange: (newLocale) => {      const localizedPath = getLocalizedUrl($page.url.pathname, newLocale);      goto(localizedPath);    },  });</script><ul class="locale-list">  {#each availableLocales as localeEl}    <li>      <a        href={getLocalizedUrl($page.url.pathname, localeEl)}        onclick={(e) => {          e.preventDefault();          setLocale(localeEl); // Will set the locale in the store and trigger onLocaleChange        }}        class:active={$locale === localeEl}      >        {getLocaleName(localeEl)}      </a>    </li>  {/each}</ul><style>  /* */</style>

(Optional) Step 10: Add backend proxy

To add a backend proxy to your SvelteKit application, you can use the intlayerProxy function provided by the vite-intlayer plugin. This plugin will automatically detect the best locale for the user based on the URL, cookies, and browser language preferences.

import { defineConfig } from "vite";import { intlayer, intlayerProxy } from "vite-intlayer";import { sveltekit } from "@sveltejs/kit/vite";// https://vitejs.dev/config/export default defineConfig({  plugins: [intlayer(), intlayerProxy(), sveltekit()],});

(Optional) Step 11: Set up the intlayer editor / CMS

To set up the intlayer editor, you must follow the intlayer editor documentation.

To set up the intlayer CMS, you must follow the intlayer CMS documentation.

To be able to visualize the intlayer editor selector, you will have to use the component syntax in your intlayer content.

<script lang="ts">  import { useIntlayer } from "svelte-intlayer";  const content = useIntlayer("component");</script><div>  <!-- Render content as simple content  -->  <h1>{$content.title}</h1>  <!-- Render content as a component (required by the editor) -->  <svelte:component this={$content.component} /></div>

Git Configuration

It is recommended to ignore the files generated by Intlayer.

# Ignore the files generated by Intlayer.intlayer

Go Further

• Visual Editor: Integrate the Intlayer Visual Editor to edit translations directly from the UI.
• CMS: Externalize your content management using the Intlayer CMS.