i18n.json Configuration

i18n.json is the configuration file that controls the Lingo.dev CLI and CI/CD integrations. It defines which languages to translate, where translatable content lives, and which translation backend to use.

Minimal example#

{
  "$schema": "https://lingo.dev/schema/i18n.json",
  "version": "1.15",
  "locale": {
    "source": "en",
    "targets": ["es", "fr", "ja"]
  },
  "buckets": {
    "json": {
      "include": ["locales/[locale].json"]
    }
  }
}

The $schema field enables IDE autocompletion and validation. The version field tracks the schema version for automatic migration compatibility.

Locale#

The locale section defines the source and target languages:

{
  "locale": {
    "source": "en",
    "targets": ["es", "fr", "de", "ja"]
  }
}

Language codes follow the BCP 47 standard - en, en-US, es-ES, zh-Hans, and platform-specific formats like Android's en-rUS are all supported.

To list available locale codes:

npx lingo.dev@latest show locale sources   # Available source languages
npx lingo.dev@latest show locale targets   # Available target languages

Buckets#

Buckets define file discovery patterns and processing rules. Each bucket key specifies a file format, and its value configures which files to include or exclude:

{
  "buckets": {
    "json": {
      "include": ["locales/[locale].json"],
      "exclude": ["locales/[locale]/internal.json"]
    },
    "markdown": {
      "include": ["docs/[locale]/*.md"]
    }
  }
}

Include patterns#

Include patterns use the [locale] placeholder, which resolves to your configured locale codes at runtime:

• locales/[locale].json → locales/en.json, locales/es.json
• docs/[locale]/*.md → docs/en/*.md, docs/es/*.md

Custom locale delimiters#

By default, locale codes in filenames use a dash (-) delimiter: en-US.json. To use underscores instead, pass an object with a delimiter field:

{
  "include": [
    "standard/[locale].json",
    { "path": "legacy/[locale].json", "delimiter": "_" }
  ]
}

This produces legacy/en_US.json instead of legacy/en-US.json.

Key path notation#

The lockedKeys, ignoredKeys, and preservedKeys arrays use forward slash (/) notation for nested keys and asterisk (*) for wildcards:

{
  "lockedKeys": ["brand/name", "config/*"]
}

For the full list of supported bucket types, see Supported Formats.

Provider#

The provider section configures a raw LLM provider for translation. This section is optional - when omitted, the CLI uses a localization engine on Lingo.dev.

{
  "provider": {
    "id": "openai",
    "model": "gpt-4o-mini",
    "prompt": "Translate the provided text from {source} to {target}."
  }
}

Engine connection#

To route translations through a specific localization engine, add the engineId field:

{
  "engineId": "eng_SxjMwMsfOIsvV1wh"
}

When engineId is set, every translation request applies your engine's brand voice, glossary, instructions, and model configuration automatically. If omitted and LINGO_API_KEY is set, the CLI uses the default engine in your organization.

For the full setup guide, see Connect Your Engine.

Environment variables#

Full example#

{
  "$schema": "https://lingo.dev/schema/i18n.json",
  "version": "1.15",
  "locale": {
    "source": "en",
    "targets": ["es", "fr", "de", "ja"]
  },
  "buckets": {
    "json": {
      "include": ["locales/[locale].json"],
      "lockedKeys": ["brand/name", "brand/tagline"],
      "ignoredKeys": ["internal/*"]
    },
    "markdown": {
      "include": ["docs/[locale]/*.md"]
    }
  },
  "engineId": "eng_SxjMwMsfOIsvV1wh"
}

Version migration#

The CLI automatically migrates older i18n.json configurations to the latest schema version. It creates a backup of your current file, updates the schema, and preserves all settings. No manual intervention is required.

Next Steps#