Pseudolocalization is the process of using mock translations to aid in the testing of UI adaption and responsiveness to localized text.

This package contains several implementations of pseudolocalizing ICU strings. Some implementations are ported from @formatjs/cli

There are three techniques to pseudolocalize text:

  • Accents (for example, “Lōrêm ípsüm”): Applies accents and diacritics to some characters. Not only does this help engineers clearly identify when text is pseudolocalized, it can also help identify issues with non-latin characters, character height and vertical space, and unsupported characters.

  • Encapsulation (for example, “[Lorem ipsum]”): Clearly identifies the start and end of text. This helps detect cases where text is being concatenated, truncated, or where text has been hard-coded.

  • Expansion (for example, “Loongeeer iiiipsuuum”): Simulates the expansion of text as it might appear in a translation. Shorter strings can expand by as much as 300%, with longer strings generally sitting somewhere between 150% and 250%. For more information, see the IBM/W3 guidelines.

Read more on my Canva Engineering blog about how to localize at scale

Available pseudo-locales

  • en-XA is ported from @formatjs/cli to test with accents technique.
  • en-XB is ported from @formatjs/cli to test with encapsulation technique.
  • en-XC is implemented using all three techniques: accents, encapsulation and expansion.
  • en-XD is similar to en-XC and friendlier to dyslexic engineers.

Given the English message my name is {name}

Locale Message
en-XA ṁẏ ńâṁè íś {name}
en-XB [!! ṁẏ ńâṁṁṁè íííś !!]Minh
en-XC မြ······ṁẏ ńâṁè íś Minh······မြ
en-XD မြ······mẏ nâmè ís Minh······မြ
  • As of 1 June 2022, code component in this table above will fail for this tall burmese character မြ

How to use

  • Simple:

import { generateENXA } from '@cungminh2710/pseudolocalize';
import IntlMessageFormat from 'intl-messageformat';

const input = 'my name is {name}';
const name = 'Minh';

console.log(new IntlMessageFormat(generateENXA(input)).format({name})); // ṁẏ ńâṁè íś {name}
  • With react-intl:

import * as React from 'react';
import * as ReactDOM from 'react-dom';
import { IntlProvider } from 'react-intl';
import { generateENXC } from '@cungminh2710/pseudolocalize';

function loadLocaleData(locale: string) {
  switch (locale) {
    case 'fr':
      return import('compiled-lang/fr.json')
      return import('compiled-lang/en.json')

function App(props) {
	const messages = React.useMemo(() => {
		if (!props.messages) return {};
		if (process.env.NODE_ENV === 'development') {
			let m: Record<string, MessageFormatElement[]> = {};
			Object.keys(props.messages).forEach((key) => {
				m[String(key)] = generateENXC(props.messages[String(key)]);
			return m;

		return props.messages;
	}, [props.messages]);

	return (
		  <MainApp />

async function bootstrapApplication(locale, mainDiv) {
  const messages = await loadLocaleData(locale)
  ReactDOM.render(<App locale={locale} messages={messages} />, mainDiv)


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