Philosophy and approach

Internationalization, or i18n, is the process of decoupling an application from a particular language or culture, and is a major requirement of most enterprise applications. As such, internationalization is one of Dojo 2’s core concerns. @dojo/i18n, Dojo 2’s internationalization ecosystem, provides everything that is needed to internationalize and localize an application, from locale-specific messaging to date, number, and unit formatting. Rather than reinvent the wheel, Dojo 2 delegates to the excellent Globalize.js library wherever possible. In addition to formatters and parsers for working with localized dates, times, numbers, and units, Globalize.js also includes an implementation of the ICU MessageFormat, which makes it possible to format messages based on locale-specific variables like gender and count. While @dojo/i18n can be used independently from the rest of Dojo 2, most applications will also rely on @dojo/widget-core and @dojo/cli-build-app to simplify internationalization.

As we will see below, the general process for internationalizing a Dojo 2 application can be outlined as follows:

  1. Set the application locale.
  2. Load any CLDR data required to correctly format values.
  3. Create message translations for all supported locales.
  4. Delegate formatting to the appropriate @dojo/i18n methods when rendering any value that may need to be localized.
  5. Update the application’s configuration settings to ensure all required data are included in the build.

Reading and setting the application’s locale

While any widget can have its own dedicated locale (see below), every Dojo 2 application has a single root locale, which can be changed at any point. By default, this root locale is set to that of the user’s environment, but can be set to a particular locale at any time. All functionality related to reading and setting the application locale is provided by @dojo/i18n/i18n.

The systemLocale property represents the environment locale, which is normalized to a valid BCP-47 language tag. Note that this differs from the format Node.js uses for process.env.LANG, from which this property is derived. i18n.locale represents the current application locale. This defaults to the environment locale, but can be changed with the switchLocale method.

import i18n, { switchLocale, systemLocale } from '@dojo/i18n/i18n';

console.log(i18n.locale === systemLocale); // true
console.log(i18n.locale); // 'ja'

Since Dojo 2 uses a reactive architecture, an observeLocale method is provided to observe changes to the application locale. It accepts an Observable whose next method is passed the new locale.

import { observeLocale, switchLocale } from '@dojo/i18n/i18n';

// Create a subscription that updates the <html> tag's "lang" attribute when
// the locale is changed.
const subscription = observeLocale({
    next: (locale: string) => {
        document.documentElement.setAttribute('lang', locale);


// destroy the observer when we no longer need to observe locale changes

Note: As you may have noticed from the previous example, changing the application locale with switchLocale does not change the <html lang> attribute. There are two reasons for this: first, DOM updates are beyond the purview of @dojo/i18n; second, the application might consist of only a portion of the total rendered DOM.

Loading CLDR data

Most functionality requires CLDR data, without which errors will be thrown. However, no CLDR data are included by Dojo 2, both due to the size of the complete CLDR data and to prevent tying applications to a specific version of the CLDR. All CLDR data must be registered with the i18n ecosystem via @dojo/i18n/cldr/load.default before the corresponding formatters can be used. This function accepts a JSON object of CLDR data. This same module also exposes an isLoaded function that can be used to determine whether specific data have been registered.

The easiest way to obtain the complete CLDR is with the cldr-data npm package, which maps the data from the Unicode repository to main and supplemental directories. The main directory houses a directory for each locale, which in turn contains all CLDR data specific to that locale. The supplemental directory contains generic data that makes more sense in standalone files, such as pluralization formats or telephone country codes.

import request from '@dojo/core/request';
import loadCldrData, { isLoaded } from '@dojo/i18n/cldr/load';

console.log(isLoaded('supplemental', 'likelySubtags')); // false
console.log(isLoaded('supplemental', 'plurals-type-cardinal')); // false

const cldrUrls = [
const cldrRequests = => {
    return request(url).then(response => response.json());

Promise.all(cldrRequests).then(results => {
    results.forEach(json => {

    console.log(isLoaded('supplemental', 'likelySubtags')); // true
    // Notice that the check is for the property on the JSON object, not the JSON filename.
    console.log(isLoaded('supplemental', 'plurals-type-cardinal')); // true

Message translations

The task most developers associate with internationalization is providing locale-specific message translations. Dojo 2 applications package translations into one or more bundles, each with a set of default translations and any number of locale-specific translations. Message loading and formatting is provided by @dojo/i18n/i18n. The default export accepts a bundle (see below) and an optional locale, and returns a promise to the loaded messages. If a locale is not provided, the root locale is assumed.

import i18n from '@dojo/i18n/i18n';
import greetings from './nls/greetings/main';

i18n(bundle, 'fr').then((messages) => {

Bundle format

Translation bundles in Dojo 2 are separated into two components: a required base module containing default values for all possible messages provided by the bundle, and individual modules for each supported locale. While not required, it is a best practice to place all message bundles under the src/nls directory. The base module must expose a default export, which must be an object, and which must contain the following:

  • An optional locales object whose keys are locales and whose values are functions that return either the locale-specific messages or a promise to the messages.
  • A messages object containing key-value pairs of default messages.

While there are no specific requirements dictating where locale-specific translations should be located, it makes the most sense to place them in directories within the same directory as their default bundle. For example, if the locales map exposed by a bundle located at src/nls/main includes both 'fr' and 'fr-CA', then the messages for those two locales might be located at src/nls/fr/main and src/nls/fr-CA/main, respectively. The default export from the locale-specific bundle modules must be an object containing the locale-specific messages as key-value pairs. Note that locale-specific bundles need not contain all possible messages; any missing messages will be filled in by the default bundle. For example, if the default bundle contains the messages { foo: 'bar', baz: 'bat' }, but a locale-specific bundle contains only { baz: 'xyzzy' }, then the default value for foo (“bar”) will be used.

For example, suppose we have a greetings bundle with default messages in English, but that also provides Arabic translations. First, we define our default bundle with a supported locales map (which, in this case, includes just Arabic):

// Default bundle: "src/nls/greetings.ts"
export default {
    locales: {
        ar: () => import('./ar/greetings')
    messages: {
        hello: 'Hello',
        helloReply: 'Hello',
        goodbye: 'Goodbye'

Second, we add the Arabic translations:

// "src/nls/ar/greetings.ts"
const messages = {
    hello: 'السلام عليكم',
    helloReply: 'و عليكم السام',
    goodbye: 'مع السلامة'
export default messages;

Finally, we use the i18n function to load the messages:

import i18n from '@dojo/i18n/i18n';
import greetings from './nls/greetings';

i18n(greetings).then((messages) => {
    console.log(message.hello); // Hello
    console.log(message.helloReply); // Hello
    console.log(message.goodbye); // Goodbye

    return i18n(greetings, 'ar');
}).then((messages) => {
    console.log(messages.hello); // 'السلام عليكم'
    console.log(messages.helloReply); // 'و عليكم السام'
    console.log(messages.goodbye); // 'مع السلامة'

Locale resolution

Locales are resolved from most to least specific. Continuing with our previous example, if the user’s locale is ar-JO (Jordanian Arabic), then the locales map provided by the default greetings bundle will be inspected for a locale exactly matching ar-JO. Since the greetings bundle does not contain translations specific to Jordanian Arabic, those provided for ar are used instead. If, however, the locale does not match any supported by the bundle, then the default messages are used.

// "src/nls/ar-JO/greetings.ts"
const messages = {
    hello: 'مرحبا',
    helloReply: 'مرحبتين'
export default messages;
import i18n, { Messages } from '@dojo/i18n/i18n';
import greetings from './nls/greetings';

i18n(greetings, 'ar-JO').then((messages) => {
    console.log(messages.hello); // 'مرحبا'
    console.log(messages.helloReply); // 'مرحبتين'

    // Since src/nls/ar-JO/greetings.ts does not specify a "goodbye" message,
    // the next best-supported value is used. In this case, the value from
    // src/nls/ar/greetings.ts is used.
    console.log(messages.goodbye); // 'مع السلامة'

    return i18n(greetings, 'cz');
}).then((messages) => {
    // Since Czech is not supported by the greetings bundle, fallback to the
    // default messages.
    console.log(messages.hello); // 'Hello'
    console.log(messages.helloReply); // 'Hello'
    console.log(messages.goodbye); // 'Goodbye'

Formatting messages

@dojo/i18n/i18n exposes two methods used to format messages: formatMessage, which can be used to format a message immediately, and getMessageFormatter, which returns a function that can be used to format the same message string multiple times with different options. Dojo 2 supports the ICU MessageFormat (see below), but that requires CLDR data, and may not be required by every application. Therefore, by default, these two methods use simple variable replacement, but switch to the more robust format once the likelySubtags and plurals-type-cardinal CLDR data have been loaded.

For example, given the message "Hello, {name}!", the formatter would be passed an object with a name string property and replace the {name} token in the message template with that passed value:

// src/nls/greetings.ts
export default {
    messages: {
        hello: 'Hello, {name}!'
import i18n, { getMessageFormatter, formatMessage } from '@dojo/i18n/i18n';
import greetings from './nls/greetings';

// First, register the bundle with `@dojo/i18n`
i18n(greetings).then(() => {
    const formatted = formatMessage(greetings, 'hello', { name: 'Margaret Mead' });
    console.log(formatted); // "Hello, Margaret Mead!"

    const formatter = getMessageFormatter(greetings, 'hello');
    console.log(formatter({ name: 'Marshall Sahlins' })); // "Hello, Marshall Sahlins!"

However, if the message needs to adapt to other variables like the number of people being addressed, then the ICU MessageFormat can be triggered by loading the likelySubtags and plurals-type-cardinal CLDR data:

// src/nls/greetings.ts
export default {
    messages: {
        hello: `{personCount, plural, offset:1
            =0: {Hello, nobody!},
            =1: {Hello, {name}!},
            other {Hello, everyone!}}`
import loadCldrData from '@dojo/i18n/cldr';
import i18n, { getMessageFormatter } from '@dojo/i18n/i18n';
import greetings from './nls/greetings';

// First, ensure the appropriate CLDR data have been loaded
[ likelySubtagsJson, pluralsJson ].map(json => loadCldrData(json));

// Next, register the bundle with `@dojo/i18n`
i18n(greetings).then(() => {
    const formatter = getMessageFormatter(greetings, 'hello');

    // "Hello, nobody!"
    console.log(formatter({ personCount: 0 }));

    // "Hello, Bill Evans!"
        name: 'Bill Evans',
        personCount: 1

    // "Hello, everyone!"
    console.log(formatter({ personCount: Infinity }));

Date, number, and unit formatting and parsing

Dojo 2 provides several helpers to facilitate formatting and parsing dates, numbers, and units for the user’s locale. As mentioned earlier, Dojo 2 relies on Globalize.js wherever possible. Since the templates for formatting and parsing data are supplied by the CLDR, each formatter and parser requires that specific CLDR data have been loaded. The exact requirements are detailed in the @dojo/i18n README.

The available formatting and parsing methods fall into two categories: those methods that accept a value and immediately return the formatted or parsed value based on the provided options, and those that return a method that can be reused to format different values based on the same options. With few exceptions noted below, each method has the same signature: a value to format or parse, an optional configuration object, and optional locale. If no locale is provided, then the root locale is assumed.

// In-place formatters:
format<T, U, V>(value: T, options?: U, locale?: string): V;
format<T, V>(value: T, locale?: string): V;

// Formatter factories:
getFormatter<T, U, V>(options?: U, locale?: string): (value: T) => V;
getFormatter<T, V>(locale?: string): (value: T) => V;

Date and time formatting

The @dojo/i18n/date module provides several functions for formatting and parsing dates and times. Each method corresponds directly to a Globalize.js method, and uses the same options available to the Globalize.js methods.

Dates are formatted and parsed according to locale-specific patterns described by the CLDR, but a variety of options are provided to control which formatting template is applied. For example, dates can be formatted solely as numerical representations, or with expanded day and month names:

import { formatDate, formatRelativeTime } from '@dojo/i18n/date';

const date = new Date(2017, 3, 1); // April 1, 2017

// Format just the date portion
formatDate(date, { date: 'short' }, 'en'); // 4/1/2017
formatDate(date, { date: 'medium' }, 'en'); // Apr 1, 2017
formatDate(date, { date: 'long' }, 'en'); // April 1, 2017
formatDate(date, { date: 'full' }, 'en'); // Saturday, April 1, 2017

// Format just the time portion
formatDate(date, { time: 'short' }, 'en'); // '3:56 AM'
formatDate(date, { time: 'medium' }, 'en'); // '3:56:42 AM'
formatDate(date, { time: 'long' }, 'en'); // '3:56:42 AM GMT-5'
formatDate(date, { time: 'full' }, 'en'); // '3:56:42 AM GMT-05:00'

// Format both the date and time portions
formatDate(date, { datetime: 'full' }, 'en'); // 'Saturday, April 1, 2017 at 3:56:42 AM GMT-05:00'
formatDate(date, { datetime: 'long' }, 'en'); // 'April 1, 2017 at 3:56:42 AM GMT-5'
formatDate(date, { datetime: 'medium' }, 'en'); // 'Apr 1, 2017, 3:56:42 AM'
formatDate(date, { datetime: 'short' }, 'en'); // '4/1/17, 3:56 AM'

// Format as relative time
formatRelativeTime(-1, 'day'); // 'yesterday'
formatRelativeTime(-1, 'week'); // 'last week'
formatRelativeTime(-1, 'week', { form: 'short' }; // 'last wk.'

Sometimes it is desirable to format multiple dates using the same options. Instead of using in-place formatters, a factory can be used, saving both energy and computational time. For example, suppose a data grid displays a list of purchases, each with their date and time. Rather than generating the correct format with each entry, the formatter can be created just once and then used as many times as needed:

import { getDateFormatter } from '@dojo/i18n/date';

const formatPurchaseDate = getDateFormatter({ datetime: 'medium' }, 'en');

class PurchaseGrid {
    // ...
    renderPurchaseDate(date: Date) {
        return formatPurchaseDate(date);

Finally, often a date will be represented as a formatted string, but is needed as a date object. For such occasions, parseDate and getDateParser can be used to read locale-specific date strings:

// Assuming all appropriate CLDR data have been loaded for French date formatting...
import { switchLocale } from '@dojo/i18n';
import { parseDate } from '@dojo/i18n/date';


parseDate('samedi, 1 avril 2017', { date: 'full' }); // Date(2017, 3, 1)

Number and currency formatting

Number and currency formatters and parsers are provided by the @dojo/i18n/number module. As with the date and time methods, each method corresponds directly to a Globalize.js method, and uses the same options available to those Globalize.js methods.

  • formatCurrency: formats a number as a currency, and delegates to Globalize.formatCurrency.
  • formatNumber: formats a number according to the specified options, and delegates to Globalize.formatNumber.
  • getCurrencyFormatter: returns a function that formats a number as a currency, and delegates to Globalize.currencyFormatter.
  • getNumberFormatter: returns a function that formats a number according to specified options, and delegates to Globalize.numberFormatter.
  • getNumberParser: returns a function that parses a number from a locale string, and delegates to Globalize.numberParser.
  • getPluralGenerator: returns a function that returns the plural group for a specified number: “zero”, “one”, “two”, “few”, “many”, or “other”, and delegates to Globalize.pluralGenerator.
  • parseNumber: parses a number from a locale string, and delegates to Globalize.parseNumber.
  • pluralize: returns the plural group for a specified number: “zero”, “one”, “two”, “few”, “many”, or “other”, and delegates to Globalize.plural.

Numbers can be formatted as currencies, percentages, or plain decimal strings, can be normalized to a specific number of significant digits, and can be rendered with or without group separators:

// Assuming all relevant CLDR data have been loaded, and that the root locale is English.
import { formatNumber, parseNumber } from '@dojo/i18n/number';

formatNumber(1234567.89); // '1,234,567.89'
formatNumber(1234567.89, 'hi-IN'); // '12,34,567.89'
formatNumber(1234567.89, 'de'); // '1.234.567,89'
formatNumber(1234567.89, { useGrouping: false }); // '1234567.89'

formatNumber(12.34, { style: 'percent' }); // '12.34%'
formatNumber(0.56, { style: 'percent' }, 'tr-TR'); // '%56'

// "12.3"
formatNumber(12.33, {
    maximumFractionDigits: 1,
    round: 'floor'

parseNumber('25 %', { style: 'percent' }); // 0.25

Finally, every language has its own rules for how words are pluralized. Some languages, such as Makonde, Igbo, and Lakota, have exactly one format regardless of count, while others have several. For example, English has exactly two formats (“1 thing”, “all the things”), while Irish Gaelic uses different forms depending on whether one item, two items, three to six items, seven to ten items, or either zero or greater than ten items are being discussed. To allow the correct form to be determined programmatically, the Unicode CLDR Project has created six different categories to describe how languages handle pluralization: “zero”, “one”, “two”, “few”, “many”, and “other”. Dojo 2 provides the pluralize method and its corresponding factory method, getPluralGenerator, to determine which category a particular number belongs to for a given locale:

// Assuming all relevant CLDR data have been loaded, and that the root locale is English.
import { switchLocale } from '@dojo/i18n/i18n';
import { pluralize } form '@dojo/i18n/pluralize';

pluralize(0); // other
pluralize(1); // one
pluralize(2); // other
pluralize(3); // other
pluralize(8); // other
pluralize(11); // other

// Change the locale to Irish

pluralize(0); // other
pluralize(1); // one
pluralize(2); // two
pluralize(3); // few
pluralize(8); // many
pluralize(11); // other

Unit formatting

@dojo/i18n/unit exposes two methods that provide locale-specific unit formatting:

The list of possible units can be found in the CLDR.

// Assuming all relevant CLDR data have been loaded
import { formatUnit } from '@dojo/i18n/unit';

formatUnit(1, 'speed-mile-per-hour'); // '1 mile per hour'
formatUnit(65, 'speed-mile-per-hour'); // '65 miles per hour'

formatUnit(1, 'foot', { form: 'long' }); // '1 foot'
formatUnit(5280, 'foot', { form: 'long' }); // '5,280 feet'
formatUnit(1, 'foot', { form: 'short' }); // '1 ft'
formatUnit(5280, 'foot', { form: 'short' }); // '5,280 ft'
formatUnit(1, 'foot', { form: 'narrow' }); // '1′'
formatUnit(5280, 'foot', { form: 'narrow' }); // '5,280′'

Internationalization with @dojo/widget-core

While @dojo/i18n is designed to be an independent package, nearly every Dojo 2 application will have a view component. So @dojo/widget-core provides a custom mixin (@dojo/widget-core/mixins/I18n) to make working with @dojo/i18n more friendly. Widgets that have incorporated this mixin can localize message bundles by passing them to the localizeBundle method during rendering. If messages for the widget’s locale have not been loaded yet, then the default messages are returned, and the widget is invalidated once the locale-specific messages have loaded. The object returned by the localizeBundle method contains all the messages, as well as a format method that takes a message key as well as any options. If message formatting is not required, then messages can be directly accessed (e.g., messages.hello).

In addition to the localizeBundle method, @dojo/widget-core/mixins/I18n introduces two properties: a boolean rtl property and a string locale property. The boolean rtl property determines whether the text decoration is right-to-left (true) or left-to-right(false: the default). The locale property specifies the locale used to determine which message translations are rendered. Since each widget can have its own distinct locale, it is possible to use multiple languages in the same application. If no locale property is included, widgets assume the root application locale (i18n.locale). Note, however, that since Dojo 2 widgets are controlled, child widgets do not automatically inherit the locale from their parent. Child widgets must receive their locale data directly from their parent widgets or from an injector; otherwise, a child widget will use the application locale while its parent uses a custom locale.

import I18nMixin, { I18nProperties } from '@dojo/widget-core/mixins/I18n';
import greetings from './nls/greetings';

export interface GreetingProperties extends I18nProperties {
    name: string;

const GreetingBase = I18nMixin(WidgetBase);
export default class Greeting extends GreetingBase<GreetingProperties> {
    render() {
        const messages = this.localizeBundle(greetings);
        const { name } =;
        const hello = messages.format('hello', { name });

        return v('p', [ hello ]);

The build process

Dojo 2 uses webpack to bundle applications. Dojo 2’s build is configured via a .dojorc at the project’s root directory. .dojorc is a JSON file containing settings defined under specific namespaces. All build options are specified under the build-app namespace, and the following are specific to internationalization:

  • locale: the default locale for the application
  • supportedLocales: an optional array of additional locales to include in the build
  • cldrPaths: an optional array of URLs for CLDR JSON to include in the build

The build ensures that the correct locale is set and all relevant CLDR data are loaded when the application starts. The user’s locale will be used if it matches either the default locale or one of the supported locales; otherwise the default locale will be used. For example, if the user’s locale is “fr-CA”, then that locale will be used if either the default locale or one of the supported locales is either “fr-CA” or “fr”.

To demonstrate what is required to set the root locale and bundle all CLDR data, suppose for our application that the default locale is English, but Spanish and French are also supported. Further, suppose that we need to support the ICU MessageFormat. All that is needed to guarantee the built application functions correctly are the following configuration settings:

// .dojorc
    "build-app": {
        "locale": "en",
        "supportedLocales": [ "es", "fr" ],
        "cldrPaths": [

With this configuration, the likelySubtags and plurals JSON will be bundled with the application and passed to the i18n ecosystem at startup, and the application locale will be set to “en”, “es”, or “fr” depending on the system locale.

Finally, since locale-specific message translations are loaded either directly or lazily with import() or require() calls that webpack can parse, they will be included in the build with no extra effort. However, since it is not always desirable to include every possible translation in the main bundle, locale-specific messages can be separated into dedicated bundles by adding their paths to the generic bundles configuration option. bundles is an object whose keys represent bundle names and whose values are arrays of modules to include in a specific bundle. For example, continuing with the previous example, suppose we would prefer to place the Spanish and French translations in their own bundles. This would be accomplished as follows:

// .dojorc
    "build-app": {
        // ...
        bundles: {
            'es': [ 'src/nls/es/main' ],
            'fr': [ 'src/nls/fr/main' ]

Now, the Spanish and French translations will be bundled separately from the main application and loaded on demand.


Internationalizing an application is not a simple task, and requires knowledge that not every developer has. While application developers must take the first step, Dojo 2 removes many of the barriers to creating a properly internationalized application, and therefore the uncertainty that an application may fail some of its users.