Recipe: Translate i18n Files

This recipe shows how to translate localization files for web and mobile apps. yaku extracts string values, translates them, and writes them back — keys and structure are never touched by the LLM.

JSON i18n files

Flat structure

Input (locales/en.json):

{
  "greeting": "Hello!",
  "farewell": "Goodbye!",
  "login": "Log in",
  "signup": "Sign up",
  "settings": "Settings"
}

yaku --to zh-TW -f locales/en.json -o locales/zh-TW.json
yaku --to ja -f locales/en.json -o locales/ja.json

Output (locales/zh-TW.json):

{
  "greeting": "你好！",
  "farewell": "再見！",
  "login": "登入",
  "signup": "註冊",
  "settings": "設定"
}

Nested structure

yaku handles deeply nested JSON:

{
  "nav": {
    "home": "Home",
    "about": "About Us"
  },
  "errors": {
    "404": "Page not found",
    "500": "Internal server error"
  }
}

yaku --to zh-TW -f en.json -o zh-TW.json

All keys, nesting, numbers, and booleans are preserved. Only string values are translated.

YAML i18n files

Rails-style i18n

Input (config/locales/en.yaml):

en:
  activerecord:
    errors:
      messages:
        blank: "can't be blank"
        invalid: "is invalid"
        taken: "has already been taken"
  views:
    pagination:
      next: "Next"
      previous: "Previous"
      first: "First"
      last: "Last"

yaku --to ja -f config/locales/en.yaml -o config/locales/ja.yaml

Output (config/locales/ja.yaml):

en:
  activerecord:
    errors:
      messages:
        blank: "空白にはできません"
        invalid: "は無効です"
        taken: "はすでに使用されています"
  views:
    pagination:
      next: "次へ"
      previous: "前へ"
      first: "最初"
      last: "最後"

Note

yaku preserves the YAML structure exactly, including the top-level en: key. You may want to rename this key to ja: manually after translation.

Batch translation

Translate one source file into multiple languages:

#!/bin/bash
SOURCE="locales/en.json"
LANGUAGES=("zh-TW" "ja" "ko" "fr" "de" "es")

for lang in "${LANGUAGES[@]}"; do
  yaku --to "$lang" -f "$SOURCE" -o "locales/${lang}.json"
  echo "Generated locales/${lang}.json"
done

Using a glossary for UI terms

UI terms often need precise, consistent translations. Create a glossary:

.yaku-glossary.yaml

zh-TW:
  Sign up: 註冊
  Log in: 登入
  Log out: 登出
  Settings: 設定
  Dashboard: 儀表板
  Profile: 個人資料

ja:
  Sign up: サインアップ
  Log in: ログイン
  Log out: ログアウト
  Settings: 設定
  Dashboard: ダッシュボード

yaku --to zh-TW -f locales/en.json -o locales/zh-TW.json
# Glossary loaded automatically from .yaku-glossary.yaml

Tips

• Translate from the source locale. Always translate from en.json (or your source language), not from another translated file.
• Use a glossary for UI consistency. Buttons, labels, and navigation items should use the same terms everywhere.
• Review pluralization. Some languages handle plurals differently. Check that plural forms are handled correctly in your i18n framework after translation.
• Watch for interpolation variables. If your i18n files contain variables like {{name}} or %{count}, verify they are preserved in the output.