i18n-localization – Writing & Content skill for AI agents

i18n & Localization

> Internationalization (i18n) and Localization (L10n) best practices.

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1. Core Concepts

| Term | Meaning |

|------|---------|

| i18n | Internationalization - making app translatable |

| L10n | Localization - actual translations |

| Locale | Language + Region (en-US, tr-TR) |

| RTL | Right-to-left languages (Arabic, Hebrew) |

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2. When to Use i18n

| Project Type | i18n Needed? |

|--------------|--------------|

| Public web app | ✅ Yes |

| SaaS product | ✅ Yes |

| Internal tool | ⚠️ Maybe |

| Single-region app | ⚠️ Consider future |

| Personal project | ❌ Optional |

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3. Implementation Patterns

React (react-i18next)

import { useTranslation } from 'react-i18next';

function Welcome() {
  const { t } = useTranslation();
  return <h1>{t('welcome.title')}</h1>;
}

Next.js (next-intl)

import { useTranslations } from 'next-intl';

export default function Page() {
  const t = useTranslations('Home');
  return <h1>{t('title')}</h1>;
}

Python (gettext)

from gettext import gettext as _

print(_("Welcome to our app"))

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4. File Structure

locales/
├── en/
│   ├── common.json
│   ├── auth.json
│   └── errors.json
├── tr/
│   ├── common.json
│   ├── auth.json
│   └── errors.json
└── ar/          # RTL
    └── ...

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5. Best Practices

DO ✅

• Use translation keys, not raw text
• Namespace translations by feature
• Support pluralization
• Handle date/number formats per locale
• Plan for RTL from the start
• Use ICU message format for complex strings

DON'T ❌

• Hardcode strings in components
• Concatenate translated strings
• Assume text length (German is 30% longer)
• Forget about RTL layout
• Mix languages in same file

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6. Common Issues

| Issue | Solution |

|-------|----------|

| Missing translation | Fallback to default language |

| Hardcoded strings | Use linter/checker script |

| Date format | Use Intl.DateTimeFormat |

| Number format | Use Intl.NumberFormat |

| Pluralization | Use ICU message format |

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7. RTL Support

/* CSS Logical Properties */
.container {
  margin-inline-start: 1rem;  /* Not margin-left */
  padding-inline-end: 1rem;   /* Not padding-right */
}

[dir="rtl"] .icon {
  transform: scaleX(-1);
}

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8. Checklist

Before shipping:

• [ ] All user-facing strings use translation keys
• [ ] Locale files exist for all supported languages
• [ ] Date/number formatting uses Intl API
• [ ] RTL layout tested (if applicable)
• [ ] Fallback language configured
• [ ] No hardcoded strings in components

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Script

The bundled checker is a heuristic, capped at 50 sorted source files. It uses English-biased regexes and directory-based JSON locale grouping; gettext catalogs and messages/en.json layouts are not fully checked for key parity. Report actual sampled/discovered counts and parse failures; a clean sample does not certify completeness, translation quality or accessibility. Mirror only directional icons for RTL (for example navigation arrows), not every logo, image or media control.

| Script | Purpose | Command |

|--------|---------|---------|

| scripts/i18n_checker.py | Detect hardcoded strings & missing translations | python scripts/i18n_checker.py <project_path> |

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.