Lingui Best Practices

Lingui is a powerful internationalization (i18n) framework for JavaScript. This skill covers best practices for implementing i18n in React and vanilla JavaScript applications.

Quick Start Workflow

The standard Lingui workflow consists of these steps:

Wrap your app in
```
I18nProvider
```
Mark messages for translation using macros (
```
Trans
```
,
```
t
```
, etc.)
Extract messages:
```
lingui extract
```
Translate the catalogs
Compile catalogs:
```
lingui compile
```
Load and activate locale in your app

Core Packages

Import from these packages:

jsx

// React macros (recommended)
import { Trans, Plural, Select, useLingui } from "@lingui/react/macro";

// Core macros for vanilla JS
import { t, msg, plural, select } from "@lingui/core/macro";

// Runtime (rarely used directly)
import { I18nProvider } from "@lingui/react";
import { i18n } from "@lingui/core";

Setup I18nProvider

Wrap your application with

I18nProvider

jsx

import { I18nProvider } from "@lingui/react";
import { i18n } from "@lingui/core";
import { messages } from "./locales/en/messages";

i18n.load("en", messages);
i18n.activate("en");

function App() {
  return (
    <I18nProvider i18n={i18n}>
      {/* Your app */}
    </I18nProvider>
  );
}

Translating UI Text

Use Trans for JSX Content

The

Trans

macro is the primary way to translate JSX:

jsx

import { Trans } from "@lingui/react/macro";

// Simple text
<Trans>Hello World</Trans>

// With variables
<Trans>Hello {userName}</Trans>

// With components (rich text)
<Trans>
  Read the <a href="/docs">documentation</a> for more info.
</Trans>

// Extracted as: "Read the <0>documentation</0> for more info."

When to use: For any translatable text in JSX elements.

Use useLingui for Non-JSX

For strings outside JSX (attributes, alerts, function calls):

jsx

import { useLingui } from "@lingui/react/macro";

function MyComponent() {
  const { t } = useLingui();

  const handleClick = () => {
    alert(t`Action completed!`);
  };

  return (
    <div>
      <img src="..." alt={t`Image description`} />
      <button onClick={handleClick}>{t`Click me`}</button>
    </div>
  );
}

When to use: Element attributes, alerts, function parameters, any non-JSX string.

Use msg for Lazy Translations

When you need to define messages at module level or in arrays/objects:

jsx

import { msg } from "@lingui/core/macro";
import { useLingui } from "@lingui/react";

// Module-level constants
const STATUSES = {
  active: msg`Active`,
  inactive: msg`Inactive`,
  pending: msg`Pending`,
};

function StatusList() {
  const { _ } = useLingui();
  
  return Object.entries(STATUSES).map(([key, message]) => (
    <div key={key}>{_(message)}</div>
  ));
}

When to use: Module-level constants, arrays of messages, conditional message selection.

Pluralization

Use the

Plural

macro for quantity-dependent messages:

jsx

import { Plural } from "@lingui/react/macro";

<Plural 
  value={messageCount}
  one="You have # message"
  other="You have # messages"
/>

The

placeholder is replaced with the actual value.

Exact Matches

Use

_N

syntax for exact number matches (takes precedence over plural forms):

jsx

<Plural
  value={count}
  _0="No messages"
  one="One message"
  other="# messages"
/>

With Variables and Components

Combine with

Trans

for complex messages:

jsx

<Plural
  value={count}
  one={`You have # message, ${userName}`}
  other={
    <Trans>
      You have <strong>#</strong> messages, {userName}
    </Trans>
  }
/>

Formatting Dates and Numbers

Use

i18n.date()

and

i18n.number()

for locale-aware formatting:

jsx

import { useLingui } from "@lingui/react/macro";

function MyComponent() {
  const { i18n } = useLingui();
  const lastLogin = new Date();
  
  return (
    <Trans>
      Last login: {i18n.date(lastLogin)}
    </Trans>
  );
}

These use the browser's

Intl

API for proper locale formatting.

Message IDs and Context

Explicit IDs

Provide a custom ID for stable message keys:

jsx

<Trans id="header.welcome">Welcome to our app</Trans>

Context for Disambiguation

When the same text has different meanings, use

context

jsx

<Trans context="direction">right</Trans>
<Trans context="correctness">right</Trans>

These create separate catalog entries.

Comments for Translators

Add context for translators:

jsx

<Trans comment="Greeting shown on homepage">Hello World</Trans>

Configuration

Basic

lingui.config.js

import { defineConfig } from "@lingui/cli";

export default defineConfig({
  sourceLocale: "en",
  locales: ["en", "es", "fr", "de"],
  catalogs: [
    {
      path: "<rootDir>/src/locales/{locale}/messages",
      include: ["src"],
      exclude: ["**/node_modules/**"],
    },
  ],
});

For detailed configuration patterns, see configuration.md.

Best Practices

Always Use Macros

Prefer macros over runtime components. Macros are compiled at build time, reducing bundle size:

jsx

// ✅ Good - uses macro
import { Trans } from "@lingui/react/macro";

// ❌ Avoid - runtime only
import { Trans } from "@lingui/react";

Keep Messages Simple

Avoid complex expressions in messages - they'll be replaced with placeholders:

jsx

// ❌ Bad - loses context
<Trans>Hello {user.name.toUpperCase()}</Trans>
// Extracted as: "Hello {0}"

// ✅ Good - clear variable name
const userName = user.name.toUpperCase();
<Trans>Hello {userName}</Trans>
// Extracted as: "Hello {userName}"

Use Trans for JSX, t for Strings

Choose the right tool:

jsx

// ✅ For JSX content
<h1><Trans>Welcome</Trans></h1>

// ✅ For string values
const { t } = useLingui();
<img alt={t`Profile picture`} />

Don't Use Macros at Module Level

Macros need component context - use

msg

instead:

jsx

// ❌ Bad - won't work
import { t } from "@lingui/core/macro";
const LABELS = [t`Red`, t`Green`, t`Blue`];

// ✅ Good - use msg for lazy translation
import { msg } from "@lingui/core/macro";
const LABELS = [msg`Red`, msg`Green`, msg`Blue`];

Use the ESLint Plugin

Install and configure

eslint-plugin-lingui

to catch common mistakes automatically:

bash

npm install --save-dev eslint-plugin-lingui

// eslint.config.js
import pluginLingui from "eslint-plugin-lingui";

export default [
  pluginLingui.configs["flat/recommended"],
];

Common Patterns

Dynamic Locale Switching

jsx

import { i18n } from "@lingui/core";

async function changeLocale(locale) {
  const { messages } = await import(`./locales/${locale}/messages`);
  i18n.load(locale, messages);
  i18n.activate(locale);
}

Loading Catalogs Dynamically

jsx

import { useEffect } from "react";
import { i18n } from "@lingui/core";

function loadCatalog(locale) {
  return import(`./locales/${locale}/messages`);
}

function App() {
  useEffect(() => {
    loadCatalog("en").then(catalog => {
      i18n.load("en", catalog.messages);
      i18n.activate("en");
    });
  }, []);
  
  return <I18nProvider i18n={i18n}>{/* ... */}</I18nProvider>;
}

Memoization with useLingui

When using memoization, use the

function from the macro version:

jsx

import { useLingui } from "@lingui/react/macro";
import { msg } from "@lingui/core/macro";
import { useMemo } from "react";

const welcomeMessage = msg`Welcome!`;

function MyComponent() {
  const { t } = useLingui(); // Macro version - reference changes with locale
  
  // ✅ Safe - t reference updates with locale
  const message = useMemo(() => t(welcomeMessage), [t]);
  
  return <div>{message}</div>;
}

Troubleshooting

If you encounter issues:

Messages not extracted: Check
```
include
```
patterns in
```
lingui.config.js
```
Translations not applied: Ensure catalogs are compiled with
```
lingui compile
```
Runtime errors: Verify
```
I18nProvider
```
wraps your app
Type errors: Run
```
lingui compile --typescript
```
for TypeScript projects

For detailed common mistakes and pitfalls, see common-mistakes.md.

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