Building “Digit Tutor” — Part 3: Internationalization

December 27th 20204 min to read

“Digit Tutor” — a simple online game for kids in Svelte, which uses speech recognition engine to train pronounciation of digits: from “0” to “9”.

✳️ Open Digit Tutor

The project is open-source, so, feel free to send a PR, if you wish!

This post is part of a series about building Digit Tutor, that include:

  1. Building “Digit Tutor” — Part 1: Svelte
  2. Building “Digit Tutor” — Part 2: Speech Recognition
  3. Building “Digit Tutor” — Part 3: Internationalization (this page)


If you’re interested in details on how “Digit Tutor” started and was built in Svelte, please, refer to the first article in the series.

The second part of the article covers speech recognition implementation details.

This one will cover intenationalization implementation, as I have implemented Russian and English support, and I also didn’t go with standard Svelte i18n implementation, since initially all resources were in a store, and it seemed to me, that Svelte store could be sufficient. And it was! I have called it “poor-man’s Svelte internationalization”.

Svelte Stores

At first, we need to understand what Svelte Stores are and how they work:

A store is simply an object with a subscribe method that allows interested parties to be notified whenever the store value changes.

Here is a simple, but feature-complete store example:

import { writable } from "svelte/store";

function createCount() {
  // this line creates a "writable" store, with "0" initial value
  // and gives subscribe, set and update methods
  // this really resembles "useState" from react
  const { subscribe, set, update } = writable(0);

  return {
    increment: () => update((n) => n + 1),
    decrement: () => update((n) => n - 1),
    reset: () => set(0),

As you can see, store does not necessarily exposes direct “set” or “update” methods — if you want to limit its updates to some specific cases (increment/decrement/reset in the sample) — this is all achievable.

There is also one more Svelte-magic with stores: you don’t actually need to use subscribe method or anything, to use store value in code or UI, just use the magic $ sign. Here is how we could use our sample store in the code:

	import { count } from './stores.js';

// this is where the magic happens, and `count` from the store
// is reactively bound to the UI
<h1>The count is {$count}</h1>

<button on:click={count.increment}>+</button>
<button on:click={count.decrement}>-</button>
<button on:click={count.reset}>reset</button>

So, stores seem to be fully sufficient to implement internaionalization:

  • It is easy to bind store values to the UI
  • Stores can expose additional logic; later I figured out, that stores can be used to logically group methods and values, just like objects from the business layer of the app
  • If store’s value is an object, it works fine if used as $store.value

Intrenationalization in a Store

My internationalization implemenetations lives in the locale.js file, and provides following features:

  • Loads initial user locale from OS settings
  • Provides list of available locales, loaded from the data-file
  • Allows to get/set current locale and its code (for the UI)

It is implemented as a writable store, whose value is an object, storing localized versions of all the strings in the app. That object is loaded from the data-file.

The store itself is used just like a usual Svelte store, which is referred as a $l in the code. Whenever selected locale changes, the underlying store object is replaced with a new one, and all UI elements change their values:

// fragment of the App.js file
{#if gameState == STARTING || gameState == NO_RECOGNITION}
  <LocaleSelector />

The Bug

Unfortunately, there was exactly one bug in the “release” version of the game, and it was connected to internationalization. Besides it, I have covered all possible corner casees with the locales, so let’s just discuss the bug.

The reason for it was, that in the LocaleSelector component, I haven’t initialized the selectedLocaleCode value the user’s OS locale. As a result, its initial value was undefined, while the UI was showing English locale as selected — just the first one in the list; at the same time, all the logic, including speech recognition, was using real user’s locale (russian, in my case).

The fix is pretty simple: I just made sure, that this variable is properly initalized in the component, too. Here is the fix, which I have done 20 minutes since the bug was reported.


It turned out, that Svelte stores is a sufficiently powerful concept to implement the internationalization. I cannot imagine anything similar from React-world, except third-party libs.

And it also turned out, that you need to be twice as thorough and attentive, when making an internationalized app, since it can be a source of additional bugs.

Anyway, I hope people liked this game, since that time I have even received multiple improvement and evolution ideas, which may some day go to production, we’ll see!