i18n

What I do

• Prepare software for multiple languages
• Handle text expansion and contraction
• Manage date, time, and number formats
• Support right-to-left (RTL) languages
• Implement locale-specific content
• Structure translation workflows

When to use me

When building applications that need to support multiple languages, regions, or cultural preferences.

Key Concepts

i18n vs l10n

i18n: Internationalization - code preparation
l10n: Localization - language/region adaptation

Implementation Patterns

// Translation keys
t('greeting', { name: 'John' })
// en.json: "Hello, {name}!"
// es.json: "¡Hola, {name}!"

// Pluralization
t('items', { count: n, plural: true })
// en: 1 item, 5 items
// ru: 1 предмет, 5 предметов

Common Libraries

# Python
from babel import Locale
from django.utils import translation

# JavaScript
import i18next from 'i18next';
import { IntlMessageFormat } from 'intl-messageformat';

# Java
import java.text.MessageFormat;
import java.util.Locale;

RTL Support

[dir="rtl"] {
  direction: rtl;
  text-align: right;
}

/* Swap left/right specific styles */
.sidebar { margin-left: 1rem; }
[dir="rtl"] .sidebar { margin-right: 1rem; }

Formatting by Locale

Dates: en-US: 1/15/2026, en-GB: 15/01/2026
Numbers: en: 1,234.56, de: 1.234,56
Currency: $1,234.56, €1.234,56

Best Practices

1. Externalize all strings
2. Use ICU message format
3. Test with pseudo-locales
4. Plan for text expansion (+30%)
5. Separate locale from logic
6. Use language codes (ISO 639-1)