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15 October 2023

Internationalization (i18n) with SvelteKit

Irelia Codeheart, Senior Developer

Understanding i18n in SvelteKit

In modern web development, internationalization (i18n) makes applications accessible to global audiences by enabling localization for different languages and regional differences.

Introduction to i18n

Internationalization (i18n), a subset of localization, is a process that makes your application adaptable to different languages, regions, and cultures, without re-engineering it. The term i18n originated from the fact that there are 18 letters between the first i and last n in 'internationalization'. In a nutshell, i18n helps your application make a global impact by reaching out to a broad user base across the world.

Why Use i18n in SvelteKit

SvelteKit, as a modern platform, provides a strong basis for building sophisticated, high-performance web applications. By implementing i18n in your SvelteKit application, it will be prepared to meet the needs of diverse audiences, which can be critical to its success. Applications that support multiple languages are more accessible, offer a better user experience, and, importantly, reach a wider potential audience.

Moreover, with the right i18n solution, managing and using translations in your SvelteKit application shouldn't be a hassle. That's where the sveltekit-i18n library comes into the picture.

Fundamentals of sveltekit-i18n Library

The sveltekit-i18n library, a lightweight internationalization solution, is specially crafted for SvelteKit projects. It is compatible with SvelteKit, supports server-side rendering (SSR), and is standalone without external dependencies.

To showcase its features, below is a brief summarization:

  • SvelteKit Compatibility: As its name suggests, this i18n library is specifically designed for SvelteKit, allowing seamless integration.

  • Server Side Rendering support: The library supports server-side rendering, offering improved performance and SEO benefits.

  • Custom Data Sources: It provides flexibility to source your translations from anywhere, such as local files or a remote API.

  • Module-Based Loading: Translations are loaded on a module basis, which means only the translations needed for visited pages will be loaded, making it very efficient.

  • Component-scoped Translations: One of the notable features is the ability to scope translations within a component, resulting in more manageable translation data.

  • Custom Modifiers: The library provides functions that can modify input data, increasing customization possibilities.

  • TypeScript Support: If your SvelteKit project is based on TypeScript, the sveltekit-i18n library is ready to use, since it's primarily written in TypeScript.

To set up sveltekit-i18n, you need to configure your translations in a particular file named translations.js. This file helps you specify the locale, the key, and the loader function for each translation. The translations can now be accessed in your SvelteKit pages and components by using the special t function offered by sveltekit-i18n.

With a rising number of stars and forks on its GitHub repository, it's evident that the sveltekit-i18n library is highly appreciated among the developer community and is undoubtedly a brilliant choice for implementing i18n in your SvelteKit applications.

In the upcoming sections, we will dive deeper into how to use sveltekit-i18n, setup translations, and explore some hands-on examples to bootstrap your understanding.

Implementing i18n with sveltekit-i18n

Through our research on SvelteKit and i18n, we found that the sveltekit-i18n library is a highly recommended, lightweight and feature-rich solution for internationalizing SvelteKit applications.

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Setting up sveltekit-i18n

Incorporating sveltekit-i18n in your application is surprisingly uncomplicated due to its SvelteKit compatibility and lack of external dependencies. The first step is to install the library via npm using the following command within your project directory:

npm install sveltekit-i18n

Following the installation, we jump onto creating a translations.js file to house our translations data. Something to note though- each translation takes the form of a locale-key-loader function tuple which can fetch translations from local files or even a remote API.

Configuring and loading translations

While configuring and loading translations, the translations.js file plays a pivotal role. An example of how to set up this file could look something as illustrated here:

// translations.js
import { loaderFunctionsFromSomewhere } from 'somewhere'

export const translations = [
     locale: 'en',
     key: 'greetings',
     loader: loaderFunctionsFromSomewhere.loadTranslation

In this example, for English locale (en), we are setting up a translation key named greetings. We fetch the relevant translations data from loaderFromSomewhere.
The loaderFunctionsFromSomewhere part can be replaced with a graphql call to caisy to fetch the translations. With caisy's forever free tier, you already get access to two different languages. Of course, this can be extended.

It's also crucial to load translations in the __layout.js file. This way, the translations are accessible in any part of the application.

Utilizing translations in components

After compiling adequate translations, we utilize them in the components using the t function provided by the sveltekit-i18n package. With the function, each component can fetch and display the appropriate locale's translations.

Here's a quick snippet to showcase how it can work:

import { t } from 'sveltekit-i18n';


In this example, {t('greetings')} fetches and displays the value for the 'greetings' key from the configured translations of the selected locale.

In summary, sveltekit-i18n is impressively flexible, and it provides a straightforward path to include intelligent internationalization in your SvelteKit projects. The library's server-side rendering support, component-scoped translations, and custom data sources ability make it a vital asset when building projects that have an international userbase outlook.

In the following sections, we will have a look at other i18n libraries suitable for SvelteKit and their implementation. Plus, we'll offer a comparison to help you make an informed choice.

Exploring the Best i18n Libraries for SvelteKit

Overview of Top i18n Libraries

When it comes to internationalization (i18n), SvelteKit offers a range of libraries to streamline your workflow. After a thorough investigation, three libraries stand out: svelte-i18n, sveltekit-i18n, and typesafe-i18n.

Key Features and Comparisons

svelte-i18n is easy to integrate and offers a straightforward setup. It's based on the well-known formatjs, offering advantages in formatting and pluralization. However, it carries a larger package size (14.2kB minified + gzipped) compared to its counterparts. It's worth noting that it isn't actively maintained, which might influence future adaptability.

Code Snippet:

import { init, getLocale, addMessages } from 'svelte-i18n';

init({ fallbackLocale: 'en' });
addMessages('en', require('./messages/en.json'));

Next is sveltekit-i18n. Explicitly made for SvelteKit with excellent SSR support, this library boasts lean translations as they are loaded only on visited pages. On top of this, it supports component-scoped translations and good TypeScript support. It is leaner in terms of size (4.6kB minified + gzipped) and is actively maintained. Understanding the syntax for its default parser for pluralization might require some special attention.

Code Snippet:

import { t, locale, _, dictionary } from '@sveltejs/sveltekit-i18n';

Finally, typesafe-i18n is a versatile library with strong Type safety and minimal dependencies. It's perfect for projects desiring precision in TypeScript and JavaScript while it's also quite lightweight. It's also actively maintained. On the flip side, getting to grips with substantially large ecosystem is somewhat a learning curve.

Code Snippet:

import { initI18n } from 'typesafe-i18n';
const { t } = initI18n({ EN: {} });

How to Choose the Right Library

Selecting the ideal i18n library must align with your project requirements. Your choice could be influenced by factors like package size, ease of integration, specific features, and the active status of the library. It's advised to prototype each library in a test application before implementing it on a large scale. This will give you a practical understanding and allow you to assess it for your particular use case.

For a robust, SvelteKit-tailored i18n solution, sveltekit-i18n could be the right choice. It offers superlative SSR support and an easy-to-use interface. If your aim is precision in TypeScript, typesafe-i18n may fit the bill. And if you simply want a minimalistic library, svelte-i18n might be the best option.

Although, every developer's "best" could vary due to their unique needs. Commit time on trialing these libraries, and you will improve your understanding of i18n in SvelteKit applications.

Diving Deep into Practical Implementation

In this section, we explore the practicalities of integrating i18n with your SvelteKit applications. We'll dive into two main areas; a comprehensive, step-by-step implementation guide, and practical examples based on actual use cases.

Complete Step by Step Implementation Guide

If you're using SvelteKit, one of the best libraries to handle internationalization is sveltekit-i18n. With its built-in support for SvelteKit, server-side rendering readiness and flexibility to handle custom data sources, it provides an ideal solution with no external dependencies. Here are the simple steps to integrate it with your application:

  1. Setting Up: After creating your SvelteKit project using degit, you'll need a translations.js file in your project's lib folder. This file will hold all translated strings and their formats.

// lib/translations.js
export const messages = {
    en: {
        welcome: 'Welcome to SvelteKit',
    fr: {
        welcome: 'Bienvenue à SvelteKit',
  1. Loading Translations: In the +layout.js file, you'll load translations based on the user's current locale and URL using the loadTranslations function.

// routes/[locale]+layout.js
import { loadTranslations } from 'sveltekit-i18n';
import { messages } from '$lib/translations.js';

  1. Accessing Translations: You can then utilize translated strings in several places using the t function.

// routes/index.svelte
import { t } from 'sveltekit-i18n';

console.log(t('welcome')); // Outputs the translated "welcome" string

Understanding Through Case Studies and Examples

Understanding i18n in SvelteKit becomes easier when we review real-life examples and use cases. Let's consider the scenario of building a product page that supports multiple languages.

Suppose you're tasked with implementing a multilingual product description page. You have a dictionary of messages with different translations for each product detail.

// lib/translations.js
export const messages = {
    en: {
        productPrice: 'Price: $100',
    fr: {
        productPrice: 'Prix: €85',

In your product page component, you would load and utilize the translations as follows:

// routes/products/index.svelte
import { t } from 'sveltekit-i18n';

console.log(t('productPrice')); // Outputs the translated "productPrice" string

Depending on the current locale, the right translation message is rendered. This way, you can use sveltekit-i18n to smoothly implement internationalization in your SvelteKit applications. It provides a robust solution, with little overhead and without increasing your application's bundle size.

Comprehensive Tutorials for SvelteKit i18n

In this section, we will delve into some of the core tutorials related to implementing internationalization (i18n) in SvelteKit. This will shed light on the key takeaways from popular tutorials along with discussing some advanced techniques and best practices.

Key Takeaways from Popular Tutorials

While working on SvelteKit applications, it's crucial to build with international audiences in mind right from the start. Famous tutorials suggest that including i18n in software architecture during the initial stages can save you massive headaches down the line.

Two libraries surface quite often for dealing with i18n in SvelteKit: svelte-i18n and i18next. svelte-i18n is a Svelte-native solution and provides functionality as a Svelte store, allowing us to leverage Svelte's reactivity features. On the other hand, i18next is a more generic solution not tied to any specific framework. It provides more advanced features, like language detection, formatting, and plurals, providing a comprehensive guide for different use cases.

A common approach is to store language information in the user's local storage or cookies. This way, the user's language preference could be remembered across site visits. Another suggestion is to handle i18n on the routing level. By prefixing the URLs with the language code (e.g., /en/dashboard), we can control the application's language.

Advanced Techniques and Best Practices

When it comes to advanced techniques in SvelteKit i18n, lazy-loading language files are recommended to reduce the initial load time. Here, we download only the required language files and load the others as needed.

A best practice is to always use keys for your translations instead of the default language text. This way, if your default language text ever changes, you don't need to change your keys. Also, remember to keep your keys consistent across your project.

While testing your i18n implementation, always make sure to include a pseudo-localized language. This mock language used for testing ensures that every text part of your application is localized correctly.

In conclusion, the application of i18n in SvelteKit is an essential skill for any developer intending to deploy global app versions. True to its nature, SvelteKit does not compromise on user experience while ensuring that your apps are accessible to all demographics.

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