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September 30, 2022 08:54
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i18n demo for Qwik

Qwik is unique in that it has fine-grained lazy loading of code. The classical way to do translation is at runtime by looking up the translation strings in the translation map. This is not conducive with lazy loading because it requires that the translations be eagerly loaded, defeating the fine-grained lazy loading of Qwik.


There are two ways to do translation:

  1. Runtime: Translation is performed at runtime by looking up the translation strings in the translation map.
    • PROS:
      • No build step.
      • Easy way to test the application in development.
    • CONS:
      • Translations strings must be eagerly loaded.
      • Each string is in triplicate. 1) original string, 2) translation string, 3) key to lookup translation string.
  2. Compile time: Translation is performed as part of the build step.
    • PROS:
      • Translated strings are inlined into the application. No need to load or look them up at runtime.
      • Because the strings are inlined, they can be lazy-loaded with application code.
    • CONS:
      • Requires a build step.
      • User can't change the language without a page refresh. (Or have mixed languages on the same page.)

We think that the best approach is to use a hybrid approach.

  1. During development, use runtime translation to make the development easy, and not require extra build steps.
  2. During production use:
    • compile time translation for code sent to the browser. It is important for the user experience to be fast only the compile-time approach can provide the best user experience.
    • runtime translation for server code. Because lazy loading is not of concern on the server, a simpler runtime approach is used. This results in a single binary that needs to be deployed to the server.

$localize (by Angular)

The translation system is based on the $localize system from Angular. The translations can be extracted in xmb, xlf, xlif, xliff, xlf2, xlif2, xliff2, and json formats.

NOTE: The $localize system is a compile-time translation system and is completely removed from the final output. $localize is a sub-project of Angular, and including its usage does not mean that Angular is used for rendering of applications.

Marking string for translation

Any string can be marked for translation by using the $localize template function like so:

export default component$((props: { name: string }) => {
  return <span>{$localize`Hello ${}!`}</span>;

Extracting string for translation

The first step in translation is to build the application. Once the artifacts are build the the strings can be extracted for translation.

npm run build.client
npm run i18n-extract

The result of the commands is src/locale/message.en.json.

Translating strings

Take the resulting string and send them for translation. Produce a file for each language. For example:

src/locale/message.en.json    # Original strings

Inline strings

The strings need to be inlined into the application. This is done automatically as part of the build.client process.

npm run build.client

The result of this command is that the browser chunks are generated once for each locale. For example:

dist/builld/q-*.js  # Original chunks

Development mode

npm run dev

Navigate to http://localhost:5173. The resulting language should match your browser language. It will pick sk if it can't detect a language, this can happen when you run under StackBlitz for example. You can also override the language by adding ?locale=fr to the URL.

Building the application

Here are the steps to build the application for production.

npm run build.client && npm run build.server && npm run i18n-translate && npm run serve

Qwik App ⚡️

Project Structure

Inside of you project, you'll see the following directories and files:

├── public/
│ └── ...
└── src/
├── components/
│ └── ...
└── routes/
└── ...

  • src/routes: Provides the directory based routing, which can include a hierarchy of layout.tsx layout files, and index.tsx files as the page. Additionally, index.ts files are endpoints. Please see the routing docs for more info.

  • src/components: Recommended directory for components.

  • public: Any static assets, like images, can be placed in the public directory. Please see the Vite public directory for more info.

Add Integrations

Use the npm run qwik add command to add other integrations. Some examples of integrations include as a Cloudflare, Netlify or Vercel server, and the Static Site Generator (SSG).

npm run qwik add


Development mode uses Vite's development server. For Qwik during development, the dev command will also server-side render (SSR) the output. The client-side development modules loaded by the browser.

npm run dev

Note: during dev mode, Vite will request many JS files, which does not represent a Qwik production build.


The preview command will create a production build of the client modules, production build of src/entry.preview.tsx, and create a local server. The preview server is only for convenience to locally preview a production build, but it should not be used as a production server.

npm run preview


The production build should generate the client and server modules by running both client and server build commands. Additionally, the build command will use Typescript run a type check on the source.

npm run build

Express Server

This app has a minimal Express server implementation. After running a full build, you can preview the build using the command:

npm run serve

Then visit http://localhost:8080/


i18n exploration






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