Build a Global Svelte App

A complete guide on how to adopt inlang with paraglide.js and message-format-plugin

Nils Jacobsen

#Build a global SvelteKit app

In this guide, we will be creating a simple SvelteKit app with i18n routing, using Paraglide for translations. This should be all you need to get started with Paraglide.

We will be using Paraglide.js, the inlang-message-format and inlang's IDE Extension.

#1. Create a SvelteKit app

Set up a SvelteKit app as you normally would. If you need help, check out the SvelteKit documentation.

npm create svelte@latest my-app
cd my-app
npm install
npm run dev
git init

#2. Initialize Paraglide

We recommend that you initialize Paraglide using the CLI. This will make sure all files are in the right place, and that the correct dependencies are installed.

In the root of your project, run:

npx @inlang/paraglide-js@latest init

The CLI might ask you some questions depending on your environment. Answer them thuroughly & follow the instructions.

npx @inlang/paraglide-js@latest init

✔ Successfully created a new inlang project.
✔ Added @inlang/paraglide-js to the dependencies in package.json.
✔ Successfully added the compile command to the build step in package.json.

 │                                                                                      │
 │  inlang Paraglide-JS has been set up sucessfully.                                    │
 │                                                                                      │
 │  1. Run your install command (npm i, yarn install, etc)                              │
 │  2. Run the build script (npm run build, or similar.)                                │
 │  3. Done :) Happy paragliding 🪂                                                     │
 │                                                                                      │
 │   For questions and feedback, visit  │
 │                                                                                      │
 │                                                                                      │

#3. Setting up the SvelteKit workspace for Paraglide

There are a few things we can do to improve our Paraglide experience when using Sveltekit.

#Adding the Vite Plugin

npm i -D @inlang/paraglide-js-adapter-vite

We import the vite adapter for paraglide, and reference the project file.

import { sveltekit } from "@sveltejs/kit/vite"
import { paraglide } from "@inlang/paraglide-js-adapter-vite"
import { defineConfig } from "vite"

export default defineConfig({
	plugins: [
			project: "./project.inlang",
			outdir: "./src/paraglide",

With the Vite-Plugin added, you can also remove the paraglide-js compile from your package.json, if you added those. The plugin will take care of that.

#Definining an Alias

Paraglide will put the translations in the ./src/paraglide folder, as specified in the vite.config.ts file. Since we will be importing from there a lot, adding an alias is a good idea.

Luckily, SvelteKit makes this super easy. It has a dedicated alias option in the kit object in svelte.config.js.

import adapter from "@sveltejs/adapter-auto"
import { vitePreprocess } from "@sveltejs/kit/vite"

/** @type {import('@sveltejs/kit').Config} */
const config = {
	preprocess: vitePreprocess(),

	kit: {
		adapter: adapter(),

		alias: {
			//You can call this whatever you want
			$paraglide: "./src/paraglide",

export default config

With the alias, we can import the translations like this:

import * as m from "$paraglide/messages"

Neat right?

#4. Adding and Using Messages

#Adding Messages

By default, paraglide uses the inlang-message-format Plugin for storing messages.

The default path for translation files are ./messages/{lang}.json. You can change this option in project.inlang.json. The Files just contain a Key-Value pair of the message ID and the message itself.

// messages/en.json
	"$schema": "",
	"hello_world": "Hello World",
	"greeting": "Hello {name}"

You can add messages in two ways:

  1. Manually editing the translation files
  2. Using the inlang IDE Extension
  • Install the ide extension from the vs-code marketplace. See extension on vs-code marketplace

  • Reload window (only needed once). ⌘ or Ctrl + Shift + P -> Developer: Reload Window. On the bottom it should display for some seconds after relaod: inlang's extension activated.

  • Select a hard-coded string, for example, on the About page. Mark the string with your cursor and hit command + . -> Inlang: Extract message. Give the message an ID and hit enter.

  • This command extracts the hard-coded string and places it into the source language translation file en.json in the messages directory.

#Using Messages

You can import messages into your code like this:

import * as m from "$paraglide/messages"

m.hello_world() // Hello World
m.greeting({ name: "John" }) // Hello John

Each message is a function that returns the message in the current language. If the message requires parameters, typescript will enforce that you pass them in.

You can change which language is currently active by using the setLanguageTag function exported from $paraglide/runtime.

import * as m from "$paraglide/messages"
import { setLanguageTag } from "$paraglide/runtime"

m.hello_world() // Hello World
m.greeting({ name: "John" }) // Hello John

m.hello_world() // Hallo Welt
m.greeting({ name: "John" }) // Hallo John

Messages are not reactive, so you will need to re-render your component when the language changes. We will see how to do that in the next step.

#5. Setting up i18n Routing

Good i18n routing is essential for a good user experience. It's also one of the most difficult things to get right. There are many ways to do it, but the following example should prepare you for most use cases.

We will be implementing the following routing structure:

  • loads the page in default language
  • loads the page in given language

#Adding a Language Parameter

First, add an optional parameter to your routes for the language. You can do this by adding double brackets to the route name. For example, [[lang]]/page.

├── +layout.svelte
└── [[lang]]
    ├── +page.svelte
    └── another-page
        └── +page.svelte

Right now [[lang]] will match any string, not just languages. We can make sure that it only matches valid language tags by adding matcher. Add a lang matcher in ./src/params/lang.ts.

// ./src/params/lang.ts
import { availableLanguageTags, AvailableLanguageTag } from "$paraglide/runtime"

export const match = (param: any): param is AvailableLanguageTag => {
	return availableLanguageTags.includes(param)

Then tell the route parameter to use the matcher.

├── +layout.svelte
└── [[lang=lang]]       //the second lang is the name of the matcher
    └── +page.svelte

#Using the Language Parameter

Armed with this route-parameter, the routing logic should already work, except for the language change. We need to communicate to Paraglide which language is currently active & re-render the page when it changes.

In your root layout, add some code that reactively sets the language tag based on the route parameter & rerenders if it changes.

<script lang="ts">
  import { page } from "$app/stores";
  import { setLanguageTag, sourceLanguageTag type AvailableLanguageTag } from "$paraglide/runtime";

  //Use the default language if no language is given
  $: lang = $page.params.lang as AvailableLanguageTag ?? sourceLanguageTag;
  $: setLanguageTag(lang);

{#key lang}

If you've never seen the #key block before, check out the Svelte docs for more info.

The language should now change when you navigate to a different language. You can navigate between languages by adding a language parameter to your links.

#Adding a language switcher

Language switchers are challenging, because they require us to translate the path we're currently on. Because there are so many different ways to implement i18n routing, we can't provide a one-size-fits-all solution. Regardless, you will probably need to define a route function that takes in a path (in any language), and returns the path in the specified language.

// ./src/lib/i18n-routing.ts
import {
	type AvailableLanguageTag,
} from "$paraglide/runtime"

 * Returns the path in the given language, regardless of which language the path is in.
export function route(path: string, lang: AvailableLanguageTag) {
	path = withoutLanguageTag(path)

	// Don't prefix the default language
	if (lang === sourceLanguageTag) return path

	// Prefix all other languages
	return `/${lang}${path}`

 * Returns the path without the language tag
function withoutLanguageTag(path: string) {
	const [_, maybeLang,] = path.split("/")
	if (availableLanguageTags.includes(maybeLang as AvailableLanguageTag)) {
		return rest.join("/")
	return path

We can now get the link to the current page in a different language by calling route with our current path.

<script lang="ts">
  import { availableLanguageTags } from "$paraglide/runtime";
  import { page } from "$app/stores";
  import { route } from "$lib/i18n-routing";

{#each availableLanguageTags as lang}
  <a href={route($page.url.pathname, lang)} hreflang={lang}>Change language to {lang}</a>

If you don't want to use <a> tags, you can also use the goto function from @sveltejs/kit to navigate programmatically.

<script lang="ts">
  import { availableLanguageTags } from "$paraglide/runtime";
  import { page } from "$app/stores";
  import { route } from "$lib/i18n-routing";
  import { goto } from "@sveltejs/kit";

{#each availableLanguageTags as lang}
  <button on:click={() => goto(route($page.url.pathname, lang))}>Change language to {lang}</button>

#6. SEO Considerations

On multi-language sites, it's easy to mess up your SEO. Here are a few things to keep in mind:

  1. Set the lang attribute on your <html> tag. This will help search engines understand which language your site is in.
  2. Add hreflang attributes to your <a> tags, unless it's the same language as the current page.
  3. Link to all language versions of your page using <link rel="alternate" hreflang="..." href="...">. This will help search engines find all versions of your page.

Let's implement these things in our app.

#Setting the lang attribute

We need to set the lang attribute in two places. The Server, so that it will be correct on the first render, and the client, so that it stays correct when navigating between pages. Let's start with the server.

We can set the lang attribute in hooks.server.ts by modifying the returned HTML. We can make this easier by making sure that the lang attribute has an easy-to-find placeholder. In ./src/app.html add a placeholder for the lang attribute.

<!-- ./src/app.html -->
<html lang="%lang%"></html>

Then in hooks.server.ts, replace the placeholder with the correct language.

// ./src/hooks.server.ts
export async function handle({ event, resolve }) {
	const lang = event.params.lang ?? sourceLanguageTag

	return await resolve(event, {
		transformPageChunk({ done, html }) {
			//Only do it at the very end of the rendering process
			if (done) {
				return html.replace("%lang%", lang)

If you now reload the page and inspect the HTML, you should see the correct lang attribute.

On the client, we can set the lang attribute using JS. In your root layout, add some code that reactively sets the lang attribute based on the route parameter.

<script lang="ts">
  import { page } from "$app/stores";
  import { setLanguageTag, sourceLanguageTag type AvailableLanguageTag } from "$paraglide/runtime";

  //Use the default language if no language is given
  $: lang = $page.params.lang as AvailableLanguageTag ?? sourceLanguageTag;
  $: setLanguageTag(lang);

  //Set the lang attribute on the html tag
  $: document.documentElement.lang = lang;

Now when you navigate change languages, the lang attribute should update.

If you have a mix of rtl and ltr languages, you can use the exact same technique to set the dir attribute.

#Linking to alternate language versions

What we want is to generate a <link rel="alternate" hreflang="..." href="..."> tag for each language version of the current page. Search Engines need this to differentiate between the different language versions of your page and to know which one to show to which user.

Fortunately, we already did most of the work for this when building the language switcher. We can reuse the route function to generate the correct href attribute.

Let's create a new I18NHeader component that generates the <link> tags.

<!-- ./src/lib/I18NHeader.svelte -->
<script lang="ts">
  import { availableLanguageTags } from "$paraglide/runtime";
  import { page } from "$app/stores";
  import { route } from "$lib/i18n-routing";

	{#each availableLanguageTags as lang}
		<link rel="alternate" hreflang={lang} href={route($page.url.pathname, lang)} />

A page should link to itself, so we don't need to filter out the current language.

#What's next?

You are now ready to use Paraglide!

If you have any questions, feel free to ask them in our Discord or open a discussion on GitHub.

You can view this example project on GitHub

This guide is based on paraglide-js 1.0.0-prerelease.12, plugin-message-format 2.0.0, m-function-matcher 0.5.0. and paraglide-js-adapter-vite 1.0.0-prerelease.2.

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