i18n-date-patterns

name	i18n-date-patterns
license	MIT
compatibility	Claude Code 2.1.76+.
description	Implements internationalization (i18n) in React applications. Covers user-facing strings, date/time handling, locale-aware formatting, ICU MessageFormat, and RTL support. Use when building multilingual UIs or formatting dates/currency.
context	inherit
agent	frontend-ui-developer
version	1.2.0
author	Yonatan Gross
tags	["i18n","internationalization","dayjs","dates","react-i18next","localization","rtl","useTranslation","useFormatting","ICU","Trans"]
user-invocable	false
disable-model-invocation	true
complexity	low
persuasion-type	reference
effort	low
targets	[{"library":"react-i18next","version":">=13.0.0"},{"library":"dayjs","version":">=1.11.0"}]
model	haiku
metadata	{"category":"document-asset-creation"}
allowed-tools	["Read","Glob","Grep","WebFetch","WebSearch"]
path_patterns	["**/i18n/**","**/locales/**","**/translations/**","*.locale.*"]

i18n and Localization Patterns

Overview

This skill provides comprehensive guidance for implementing internationalization in React applications. It ensures ALL user-facing strings, date displays, currency, lists, and time calculations are locale-aware.

When to use this skill:

• Adding ANY user-facing text to components
• Formatting dates, times, currency, lists, or ordinals
• Implementing complex pluralization
• Embedding React components in translated text
• Supporting RTL languages (Hebrew, Arabic)

Bundled Resources (load with Read("${CLAUDE_SKILL_DIR}/<path>")):

• references/formatting-utilities.md - useFormatting hook API reference
• references/icu-messageformat.md - ICU plural/select syntax
• references/trans-component.md - Trans component for rich text
• checklists/i18n-checklist.md - Implementation and review checklist
• examples/component-i18n-example.md - Complete component example

Canonical Reference: See docs/i18n-standards.md for the full i18n standards document.

---

Core Patterns

1. useTranslation Hook (All UI Strings)

Every visible string MUST use the translation function:

import { useTranslation } from 'react-i18next';

function MyComponent() {
  const { t } = useTranslation(['patients', 'common']);
  
  return (
    <div>
      <h1>{t('patients:title')}</h1>
      <button>{t('common:actions.save')}</button>
    </div>
  );
}

2. useFormatting Hook (Locale-Aware Data)

All locale-sensitive formatting MUST use the centralized hook:

import { useFormatting } from '@/hooks';

function PriceDisplay({ amount, items }) {
  const { formatILS, formatList, formatOrdinal } = useFormatting();
  
  return (
    <div>
      <p>Price: {formatILS(amount)}</p>        {/* ₪1,500.00 */}
      <p>Items: {formatList(items)}</p>        {/* "a, b, and c" */}
      <p>Position: {formatOrdinal(3)}</p>      {/* "3rd" */}
    </div>
  );
}

Load Read("${CLAUDE_SKILL_DIR}/references/formatting-utilities.md") for the complete API.

3. Date Formatting

All dates MUST use the centralized @/lib/dates library:

import { formatDate, formatDateShort, calculateWaitTime } from '@/lib/dates';

const date = formatDate(appointment.date);    // "Jan 6, 2026"
const waitTime = calculateWaitTime('09:30');  // "15 min"

4. ICU MessageFormat (Complex Plurals)

Use ICU syntax in translation files for pluralization:

{
  "patients": "{count, plural, =0 {No patients} one {# patient} other {# patients}}"
}

t('patients', { count: 5 })  // → "5 patients"

Load Read("${CLAUDE_SKILL_DIR}/references/icu-messageformat.md") for full syntax.

5. Trans Component (Rich Text)

For embedded React components in translated text:

import { Trans } from 'react-i18next';

<Trans
  i18nKey="richText.welcome"
  values={{ name: userName }}
  components={{ strong: <strong /> }}
/>

Load Read("${CLAUDE_SKILL_DIR}/references/trans-component.md") for patterns.

---

Translation File Structure

frontend/src/i18n/locales/
├── en/
│   ├── common.json      # Shared: actions, status, time
│   ├── patients.json    # Patient-related strings
│   ├── dashboard.json   # Dashboard strings
│   ├── owner.json       # Owner portal strings
│   └── invoices.json    # Invoice strings
└── he/
    └── (same structure)

---

Anti-Patterns (FORBIDDEN)

// ❌ NEVER hardcode strings
<h1>מטופלים</h1>                    // Use t('patients:title')
<button>Save</button>               // Use t('common:actions.save')

// ❌ NEVER use .join() for lists
items.join(', ')                    // Use formatList(items)

// ❌ NEVER hardcode currency
"₪" + price                         // Use formatILS(price)

// ❌ NEVER use new Date() for formatting
new Date().toLocaleDateString()     // Use formatDate() from @/lib/dates

// ❌ NEVER use inline plural logic
count === 1 ? 'item' : 'items'      // Use ICU MessageFormat

// ❌ NEVER leave console.log in production
console.log('debug')                // Remove before commit

// ❌ NEVER use dangerouslySetInnerHTML for i18n
dangerouslySetInnerHTML             // Use <Trans> component

---

Quick Reference

Need	Solution
UI text	t('namespace:key') from useTranslation
Currency	formatILS(amount) from useFormatting
Lists	formatList(items) from useFormatting
Ordinals	formatOrdinal(n) from useFormatting
Dates	formatDate(date) from @/lib/dates
Plurals	ICU MessageFormat in translation files
Rich text	<Trans> component
RTL check	isRTL from useFormatting

---

Checklist

Load Read("${CLAUDE_SKILL_DIR}/checklists/i18n-checklist.md") for complete implementation and review checklists.

---

Integration with Agents

Frontend UI Developer

• Uses all i18n patterns for components
• References this skill for formatting
• Ensures no hardcoded strings

Code Quality Reviewer

• Checks for anti-patterns (.join(), console.log, etc.)
• Validates translation key coverage
• Ensures RTL compatibility

---

Skill Version: 1.2.0 Last Updated: 2026-01-06 Maintained by: Yonatan Gross

Related Skills

• ork:testing-e2e - E2E testing patterns including accessibility testing for i18n
• type-safety-validation - Zod schemas for validating translation key structures and locale configs
• ork:react-server-components-framework - Server-side locale detection and RSC i18n patterns
• ork:accessibility - RTL-aware focus management for bidirectional UI navigation

Key Decisions

Decision	Choice	Rationale
Translation Library	react-i18next	React-native hooks, namespace support, ICU format
Date Library	dayjs	Lightweight, locale plugins, immutable API
Message Format	ICU MessageFormat	Industry standard, complex plural/select support
Locale Storage	Per-namespace JSON	Code-splitting, lazy loading per feature
RTL Detection	CSS logical properties	Native browser support, no JS overhead

Capability Details

translation-hooks

Keywords: useTranslation, t(), i18n hook, translation hook Solves:

• Translate UI strings with useTranslation
• Implement namespaced translations
• Handle missing translation keys

formatting-hooks

Keywords: useFormatting, formatCurrency, formatList, formatOrdinal Solves:

• Format currency values with locale
• Format lists with proper separators
• Handle ordinal numbers across locales

icu-messageformat

Keywords: ICU, MessageFormat, plural, select, pluralization Solves:

• Implement pluralization rules
• Handle gender-specific translations
• Build complex message patterns

date-time-formatting

Keywords: date format, time format, dayjs, locale date, calendar Solves:

• Format dates with dayjs and locale
• Handle timezone-aware formatting
• Build calendar components with i18n

rtl-support

Keywords: RTL, right-to-left, hebrew, arabic, direction Solves:

• Support RTL languages like Hebrew
• Handle bidirectional text
• Configure RTL-aware layouts

trans-component

Keywords: Trans, rich text, embedded JSX, interpolation Solves:

• Embed React components in translations
• Handle rich text formatting
• Implement safe HTML in translations