Internationalization (i18n) with SvelteKit

Are you able to create multilingual web apps?

In 2025, you better make sure you are!

In modern web development, internationalization (i18n) makes applications accessible to global audiences through localization for different languages and regional differences.This guide will help you master internationalization (i18n) in SvelteKit. We'll walk you through setting up, configuring, and using i18n in SvelteKit with practical examples and advanced techniques. By the end, you'll have the tools to efficiently manage translations and offer a seamless user experience. Let's dive into the world of SvelteKit i18n and unlock your app's full potential!

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How does i18n work?

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.

It involves using translation files and dynamic content to serve users in their native language. This is crucial because it enhances user experience, expands your audience, and meets global market demands. In a world where digital presence spans across borders, i18n ensures your app is inclusive and user-friendly, boosting engagement and satisfaction. Investing in i18n ultimately drives growth and accessibility.

Learn more about the many benefits of localization.

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. Here are the benefits of using Typescript.

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.

Why Use i18n in SvelteKit?

SvelteKit, as a modern platform, offers a robust foundation for building high-performance web applications. Implementing i18n (internationalization) in your SvelteKit application is crucial for several reasons.

Internationalization in SvelteKit can be efficiently managed with libraries like sveltekit-i18n and svelte-i18n. These libraries simplify the process of loading translations, managing locale changes, and integrating language-specific content, making it easier for developers to maintain and scale their applications​.

Recent updates in SvelteKit, such as improved SSR (Server-Side Rendering) support and enhanced routing capabilities, further streamline the process of building multilingual websites​​. By leveraging these features, you can ensure your application not only meets user expectations but also adheres to best practices in web development and SEO .

Incorporating i18n in your SvelteKit project is a strategic move that promotes user satisfaction, boosts engagement, and drives growth in the international market.

Setting Up SvelteKit for i18n

Prerequisites

Before you start the svelte i18n journey, ensure you have the following prerequisites:

• Node.js and npm: Make sure you have Node.js and npm installed. You can download them from nodejs.org.

• SvelteKit Project: Set up a basic SvelteKit project. If you haven't done this yet, run the following commands to create a new SvelteKit app:

  npm init svelte@next my-sveltekit-app
  cd my-sveltekit-app
  npm install

Installing Necessary Packages

To implement i18n in your SvelteKit application, you'll need to install the svelte-i18n library we already talked about:

Install svelte-i18n:

npm install svelte-i18n

Initial Project Setup

1. Create Translation Files:

   1. Create a directory named locales in your src folder.

   2. Inside the locales folder, create JSON files for each language you want to support, for example, en.json and es.json.

   Example of en.json:

   {
     "greeting": "Hello",
     "farewell": "Goodbye"
   }

   
   
   

   Example of es.json:

   {
     "greeting": "Hola",
     "farewell": "Adiós"
   }
   

   
   
   

2. Configure svelte-i18n:

   Create a new file named i18n.js in your src directory and add the following configuration:

   import { init, register, getLocaleFromNavigator } from 'svelte-i18n';
   
   register('en', () => import('./locales/en.json'));
   register('es', () => import('./locales/es.json'));
   
   init({
     fallbackLocale: 'en',
     initialLocale: getLocaleFromNavigator(),
   });

   
   
   

3. Initialize i18n in Your Application:

   Import and initialize the i18n setup in your __layout.svelte file or the main entry point of your application:

   import './i18n';

   
   
   

4. Using Translations in Components

   1. Import the $t Store: Import the translation store in your Svelte component.

      ht<script>
        import { $t } from 'svelte-i18n';
      </script>

      
      

   2. Use Translation Keys: Use the $t store to access translation keys in your component's template.

      <h1>{$t('greeting')}</h1>
      <p>{$t('farewell')}</p>

      
      

   By following these steps, you will have a basic SvelteKit application set up with internationalization support – Yeah! 🎉

   
   

Diving Deep into Practical Implementation

Complete Step-by-Step Implementation Guide

To effectively integrate i18n in your SvelteKit application, follow these steps using the sveltekit-i18n library, known for its built-in support for SvelteKit and server-side rendering readiness.

1. Setting Up: After creating your SvelteKit project using degit, create 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',
       }
   };
   

   
   
   

2. Loading Translations: In the +layout.js file, 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';
   
   loadTranslations(messages);
   

   
   
   

3. Accessing Translations: Utilize translated strings in various parts of your application using the t function.

   <!-- routes/index.svelte -->
   <script>
       import { t } from 'sveltekit-i18n';
   </script>
   
   <h1>{$t('welcome')}</h1>
   

   
   

   By following these steps, you can implement practical i18n functionality in your SvelteKit application, ensuring a better user experience for a global audience. Now it's time to look at some more advanced methods.

Advanced i18n Techniques

Dynamic Loading of Translations

Dynamic loading allows your application to load translation files only when needed. This has a possitive effect on the performance and reduces initial load time.

1. Setup Dynamic Imports: Modify your i18n.js configuration to use dynamic imports:

   import { init, register, getLocaleFromNavigator } from 'svelte-i18n';
   
   register('en', () => import('./locales/en.json'));
   register('es', () => import('./locales/es.json'));
   
   init({
     fallbackLocale: 'en',
     initialLocale: getLocaleFromNavigator(),
     loadingDelay: 200,
     formats: {},
     warnOnMissingMessages: true
   });
   

   
   
   

2. Load Translations on Demand: Ensure translations are loaded dynamically based on the current route or user action. This can be integrated into your route files or component logic.

Handling Right-to-Left (RTL) Languages

Supporting RTL languages like Arabic or Hebrew involves additional CSS and layout considerations.

1. CSS Adjustments: Add CSS rules to handle RTL layouts:

   [dir="rtl"] {
     direction: rtl;
     text-align: right;
   }
   

   
   

2. Dynamic Direction Handling: Dynamically set the dir attribute based on the selected language:

   import { locale, waitLocale } from 'svelte-i18n';
   
   $: {
     document.dir = $locale === 'ar' || $locale === 'he' ? 'rtl' : 'ltr';
   }

   
   

Custom i18n Adapters

Custom adapters allow you to fetch translations from different sources such as APIs or databases.

1. Create Custom Adapter: Implement a custom adapter for fetching translations:

   
   import { init, getLocaleFromNavigator } from 'svelte-i18n';
   
   const fetchTranslations = async (locale) => {
     const response = await fetch(`/api/translations?locale=${locale}`);
     return response.json();
   };
   
   init({
     fallbackLocale: 'en',
     initialLocale: getLocaleFromNavigator(),
     async fetchMessages({ locale }) {
       return await fetchTranslations(locale);
     }
   });
   

   
   

2. Integrate with Backend: Ensure your backend API can provide the necessary translation files based on the locale requested.

By incorporating these advanced techniques, your SvelteKit application will be better equipped to handle complex internationalization needs, providing a seamless user experience across different languages and regions

Case Studies and Examples

Understanding i18n in SvelteKit becomes easier when we review real-life examples and use cases.

Case Study: Community-Driven Localization with SvelteKit

A developer shared their experience about using svelte-i18n, sveltekit-i18n, and typesafe-i18n to localize applications. The post highlighted the following key points:

1. Library Selection: The developer compared different libraries (svelte-i18n, sveltekit-i18n, and typesafe-i18n), each offering unique features like SSR support, synchronous and asynchronous loading of translations, and ICU message syntax.

2. Ease of Use: It was noted that svelte-i18n integrates seamlessly with Svelte’s ecosystem, making it easy to implement. However, sveltekit-i18n was preferred for its active maintenance and better support for SvelteKit’s SSR capabilities.

For more details, visit the full post on DEV Community.

Example: Building a multilingual product page

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.

Common Errors and Solutions

Error 1: Missing Translation Keys

Solution: If you encounter missing translation keys, ensure that all keys exist in your translation files. Use the warnOnMissingMessages option in your init configuration to log warnings for missing translations:

import { init, register, getLocaleFromNavigator } from 'svelte-i18n';

register('en', () => import('./locales/en.json'));
register('es', () => import('./locales/es.json'));

init({
  fallbackLocale: 'en',
  initialLocale: getLocaleFromNavigator(),
});

This helps you identify and fix missing keys promptly.

Error 2: Incorrect Locale Detection

Solution: If your application is not detecting the correct locale, verify that you are using getLocaleFromNavigator() correctly. Ensure the browser’s language settings are properly configured and your translation files are named accurately. You can also manually set the locale if needed:

import { locale } from 'svelte-i18n';

locale.set('en');

Error 3: Performance Issues with Large Translation Files

Solution: For large translation files, use dynamic loading and split translations into smaller chunks. This reduces the initial load time and improves performance:

register('en', () => import('./locales/en.json'));
register('es', () => import('./locales/es.json'));

Additionally, ensure translations are loaded only for the current page or component to minimize the load.

Error 4: Issues with Server-Side Rendering (SSR)

Solution: Ensure that your i18n setup is compatible with SSR. Libraries like sveltekit-i18n are designed to work well with SSR. Make sure you configure the library correctly and handle locale settings on the server side.

For more detailed troubleshooting and advanced solutions, refer to the official documentation and community resources:

• svelte-i18n Documentation​

• Reddit Discussion on SvelteKit i18n​

• Phrase Guide on Localizing Svelte Apps​

By addressing these common issues and following best practices, you can ensure a smooth and effective i18n implementation in your SvelteKit application.

Conclusion of sveltekit i18n guide

Recap of Key Points

In this article, we covered the essentials of implementing internationalization (i18n) in SvelteKit. We started with the basics, setting up your project and configuring svelte-i18n for multiple languages. We then explored advanced techniques, such as dynamic loading of translations, handling right-to-left languages, and creating custom i18n adapters. Practical case studies and examples illustrated real-world applications, providing valuable insights into effective i18n strategies. Lastly, we addressed common issues and troubleshooting tips to ensure a smooth integration process.

Encouragement to Implement i18n in Projects

Implementing i18n in your SvelteKit projects is a strategic move that enhances user experience and broadens your audience reach. By making your application accessible in multiple languages, you cater to a diverse user base and meet global market demands. Whether you're building an e-commerce platform, an educational site, or a personal blog, integrating i18n can significantly improve engagement and satisfaction.

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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