ai-l10n

AI-powered translation for app localization. Automatically translate your i18n files to 165 languages using AI. Supports JSON, JSONC, Flutter ARB, YAML, PO, XLIFF, and all other text-based localization formats with intelligent project structure detection.

ai-localization example

Features

One command turns your source file into 165 languages — from the CLI, an npm script, your CI pipeline, or your AI agent. No pasting files into a chat window, no broken placeholders, no re-translating everything because one string changed.

bash

npx ai-l10n translate ./locales/en.json --update

Translate

🤖 165 languages — context-aware AI translation, not word-by-word machine output
🎯 Any text-based format — JSON, JSONC, Flutter ARB, Shopify themes, YAML, PO (gettext), XLIFF, and more (full list)
📁 Zero setup — target languages are auto-detected from your file and folder layout
🔄 Incremental by default — --update translates only new and changed strings and leaves the rest untouched

Quality you can ship

🛠️ Nothing breaks — placeholders, HTML tags, and formatting are preserved; dates and numbers are localized; proper names, URLs, and technical terms are left alone (how it works)
🌐 Correct plural forms — every i18next suffix is generated, including complex rules in Russian, Arabic, and Polish
🔒 Type-safe JSON — numbers stay numbers, booleans stay booleans, null stays null
📚 Glossary & terminology — lock brand, legal, and product terms so the AI can't pick a synonym
✍️ Linguistic instructions — set tone and style once, e.g. --instruction "Use formal tone"

Built for automation

⚙️ Runs anywhere — CLI, SDK, npm scripts, GitHub Action, GitLab CI, Jenkins, and MCP for AI agents
🕵️ Self-checking — detects lost placeholders and retries; splits large files into chunks while keeping context, avoiding the silent content loss you get pasting strings into Claude or GPT
🔍 Content filtering — filtered strings are saved to a separate file for review instead of failing the run
📊 Usage tracking — monitor character usage and balance; 10,000 characters free every month, pay-as-you-go after that

Installation

For CLI + Programmatic (SDK)

bash

npm install ai-l10n

For AI Agents (MCP Server)

Use the ai-l10n-mcp package to connect AI agents (Claude Desktop, Cursor, Windsurf, GitHub Copilot, OpenAI Codex) directly to l10n.dev. See the MCP server README for configuration instructions.

json

{
  "mcpServers": {
    "l10n": {
      "command": "npx",
      "args": ["-y", "ai-l10n-mcp"]
    }
  }
}

For SDK Only

bash

npm install ai-l10n-sdk

Getting Started

1. Get Your API Key

Get your free API key from l10n.dev/ws/keys

2. Configure API Key

You can provide your API key in three ways:

Option A: Save it globally

bash

npx ai-l10n config --api-key YOUR_API_KEY

Option B: Use environment variable

bash

export L10N_API_KEY=your_api_key_here

Option C: Pass it directly in code or CLI

bash

npx ai-l10n translate path/to/file.json --api-key YOUR_API_KEY

3. Translate Your Files

Basic Translation

bash

# Auto-detect target languages from project structure
npx ai-l10n translate path/to/en.json

# Specify target languages
npx ai-l10n translate path/to/en.json --languages es,fr,de

# Update existing files with only new translations
npx ai-l10n translate path/to/en.json --update

Advanced Options

bash

npx ai-l10n translate ./locales/en.json \
  --languages es,fr,de \
  --plural \                    # Generate plural forms (adds suffixes, e.g., for i18next)
  --shorten \                   # Use shortening
  --no-contractions \           # Don't use contractions (e.g., "don't" vs "do not")
  --update \                    # Update existing files (translates only new and changed strings)
  --replace \                   # Replace existing files (rewrites file with new translations, overwise it adds a copy number e.g., `es (1).json`)
  --glossary \                  # Generate and save glossary for future translations
  --instruction "Be formal" \   # Control the overall style, tone, and translation behavior
  --language-regex "^emails\.(?<language>[\w-]+)\.json$" \  # Locate the language code in file names
  --verbose                     # Detailed logging

Batch Translation

Create a config file translate-config.json:

json

[
  {
    "sourceFile": "./locales/en/common.json",
    "targetLanguages": ["pl", "ru", "ar"],
    "generatePluralForms": true,
    "translateOnlyNewStrings": true
  },
  {
    "sourceFile": "./locales/en/admin.json",
    "targetLanguages": ["pl", "ru", "ar", "de"],
    "replace": true
  }
]

Run batch translation:

bash

npx ai-l10n batch translate-config.json

Configuration Management

bash

# View current API key status
npx ai-l10n config

# Set API key
npx ai-l10n config --api-key YOUR_API_KEY

# Clear API key
npx ai-l10n config --clear

Programmatic Usage

typescript

import { AiTranslator } from 'ai-l10n';

const translator = new AiTranslator();

const result = await translator.translate({
  sourceFile: './locales/en.json',
  targetLanguages: ['es', 'fr', 'de'],
});

📚 See the ai-l10n-sdk README for:

Complete API documentation and TypeScript interfaces
Advanced usage examples
Custom logger integration
Error handling and type definitions

NPM Scripts Integration

Add scripts to your package.json:

json

{
  "scripts": {
    "translate": "ai-l10n translate ./locales/en.json",
    "translate:update": "ai-l10n translate ./locales/en.json --update",
    "translate:replace": "ai-l10n translate ./locales/en.json --replace",
    "translate:all": "ai-l10n batch translate-config.json"
  }
}

Then run:

bash

npm run translate
npm run translate:update
npm run translate:replace
npm run translate:all

CI/CD Integration

GitHub Actions

ai-l10n provides a ready-to-use GitHub Action for automated translations. The action uses the batch command with a config file for flexible, multi-file translation workflows.

Quick Setup:

Create a translation config file ai-l10n.config.json in your repository root:

json

[
  {
    "sourceFile": "./locales/en/common.json",
    "targetLanguages": ["es", "fr", "de"],
    "translateOnlyNewStrings": true
  }
]

Add the workflow file:

yaml

name: Auto-translate i18n files

on:
  push:
    branches:
      - main
    paths:
      - 'locales/en.json'
      - 'locales/en/**'
      - 'ai-l10n.config.json'

permissions:
  contents: write

jobs:
  translate:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      
      - uses: l10n-dev/ai-l10n@v1
        with:
          api-key: ${{ secrets.L10N_API_KEY }}
          config-file: 'ai-l10n.config.json'
          pull-request: false

Action Inputs:

Input	Description	Default	Required
`version`	L10n.dev CLI version	`latest`	No
`api-key`	L10n.dev Platform API Key	-	No (can use `L10N_API_KEY` env var)
`github-token`	GitHub token for PR creation (optional if repo setting enabled)	`github.token`	No
`config-file`	Path to translation config file	`ai-l10n.config.json`	No
`pull-request`	Create PR instead of direct commit	`false`	No
`commit-message`	Commit message	`feat: update translations via L10n.dev`	No
`pull-request-title`	Pull request title	`feat: update translations via L10n.dev`	No
`commit-author-name`	Git commit author name	`L10n.dev`	No
`commit-author-email`	Git commit author email	`support@l10n.dev`	No
`process-own-commits`	Process commits made by this action	`false`	No
`working-directory`	Working directory (for monorepos)	`.`	No
`skip-setup-node`	Skip Node.js setup if already installed	`false`	No

ℹ️ Note on Pull Requests: To use pull-request: true, you have two options:

Enable repository setting (recommended): Go to Settings > Actions > General and enable "Allow GitHub Actions to create and approve pull requests"

Use Personal Access Token: Provide a PAT with repo scope via github-token input

📚 More Examples:

Pull Request workflow - Creates PR for review (recommended for main/master)
Direct Commit workflow - Commits directly (for feature branches)
Manual Trigger workflow - Run manually with custom inputs

GitLab CI

yaml

translate:
  stage: build
  script:
    - npm install
    - npx ai-l10n translate ./locales/en.json --update
  only:
    changes:
      - locales/en.json
  variables:
    L10N_API_KEY: $L10N_API_KEY

Jenkins

groovy

pipeline {
  agent any
  
  environment {
    L10N_API_KEY = credentials('l10n-api-key')
  }
  
  stages {
    stage('Translate') {
      steps {
        sh 'npm install'
        sh 'npx ai-l10n translate ./locales/en.json --update'
      }
    }
  }
}

Project Structure

ai-l10n automatically detects your project structure and generates translations accordingly.

Folder-Based Structure

locales/
  en/
    common.json
    errors.json
  es/                  # Auto-detected
    common.json
    errors.json
  zh-Hans-CN/          # Auto-detected
    common.json

File-Based Structure (JSON)

locales/
  en.json              # Source
  es.json              # Auto-detected
  fr-FR.json           # Auto-detected
  zh-Hans-CN.json      # Auto-detected

File-Based Structure (Flutter ARB)

lib/l10n/
  app_en.arb           # Source
  app_es.arb           # Auto-detected
  app_fr_FR.arb        # Auto-detected
  app_zh_Hans_CN.arb   # Auto-detected

Language Code Inside the File Name

The language code may also sit next to other parts of the file name. Files following the same naming pattern are detected, and target files keep that pattern:

locales/
  emails.en.json       # Source                -> emails.ru-RU.json
  emails.es.json       # Auto-detected
  en-US.common.json    # Source                -> ja.common.json
  emails-en.json       # Source                -> emails-fr.json
  common.en-Latn-US.yml
  messages_en_US.properties  # Source          -> messages_ru_RU.properties

Every part of the code is validated against the known ISO language, script and region codes, so ordinary file names such as strings.min.json or config.dev.json are not mistaken for localization files. For naming conventions that are not recognized, describe them with languageCodeRegex (--language-regex on the CLI):

bash

ai-l10n translate locales/emails.en.json -l ru-RU \
  --language-regex "^emails\.(?<language>[\w-]+)\.json$"

The pattern must contain a (?<language>...) group; the text before and after it is reused to find files of other languages and to build target file names.

Configuration Options

Option	Type	Default	Description
`sourceFile`	`string`	required	Path to source file. Supports JSON, JSONC, ARB, YAML, PO, XLIFF, and all other text-based formats. See the full supported formats list
`targetLanguages`	`string[]`	auto-detect	Target language codes (e.g., `["es", "fr", "de"]`)
`apiKey`	`string`	env/stored	API key for l10n.dev
`generatePluralForms`	`boolean`	`false`	Generate plural forms with suffixes (e.g., for i18next). Don't use for strict source-to-target mapping
`useShortening`	`boolean`	`false`	Use shortening in translations
`useContractions`	`boolean`	`true`	Use contractions in translations (using contractions makes the translation less formal)
`translateMetadata`	`boolean`	`false`	Translate metadata along with UI strings. For example, in Flutter ARB files, metadata entries like @key contain descriptions that can also be translated. Disabling this option ensures that metadata remains unchanged in the target files
`saveFilteredStrings`	`boolean`	`true`	Save filtered strings (i18n JSON format with source strings excluded due to content policy violations) to a separate `.filtered` file
`translateOnlyNewStrings`	`boolean`	`false`	Update existing files with only new/changed translations. When `true`, we store hashes of source strings (without text itself), so the system can detect which strings are new vs. old based on the presence of their hashes.
`replace`	`boolean`	`false`	Replace existing files with new translations, overwise if the target file already exists it adds a copy number (e.g., `es (1).json`)
`verbose`	`boolean`	`false`	Enable detailed logging
`sourceLanguageCode`	`string \| null`	auto-detect	BCP-47 source language code (e.g., `"en"`, `"en-US"`). Auto-detected from the file path when not set
`languageCodeRegex`	`string`	auto-detect	Regex locating the language code in file names, e.g. `"^emails\\.(?<language>[\\w-]+)\\.json$"`. Must contain a `(?<language>...)` group; the text around it is reused for target file names. Only needed when the naming convention is not detected automatically. CLI: `--language-regex`
`generateGlossary`	`boolean`	`false`	Generate and save a glossary from source and translated content for this language pair. Balance debited upfront for full source content. See Translation Glossary
`glossary`	`GlossaryEntry[] \| null`	use active	Override the active glossary: `null`/omit = use active, `[]` = disable, entries = replace for this request
`instruction`	`string \| null`	use active	Override the active linquistic instruction: `null`/omit = use active, = disable, `string` = replace for this request
`terminology`	`TerminologyEntry[]`	none	Terms for consistent translation — synonyms are replaced with the preferred term

Content Filtering

The service uses automated content filtering systems configured at moderate sensitivity levels to balance safety with service availability. When content is filtered:

Filtered strings are saved in i18n JSON format to a .filtered file (if saveFilteredStrings is enabled)
Content filtering operates automatically and does not constitute editorial control over your content

If strings are filtered, you'll see:

⚠️ Some strings were excluded due to content policy violations
ℹ️ View content policy at: https://l10n.dev/terms-of-service#content-policy
📝 Filtered strings saved to: path/to/file.filtered.json

Translation Glossary

A translation glossary maps specific source-language terms to approved target-language equivalents, ensuring the AI uses your exact terminology instead of valid-but-unintended synonyms. Glossaries are especially valuable for brand names, legal terms, clinical vocabulary, and product-specific concepts.

AI Glossary Generation (`--glossary` / `generateGlossary`)

Use --glossary (CLI) or generateGlossary: true (config) to automatically build a glossary from the source and translated target content, then save it as the active glossary for this source/target language pair:

bash

npx ai-l10n translate ./locales/en.json --languages de,fr --glossary

Once saved, the glossary is applied automatically on all future translations for the same language pair. Manage your saved glossaries at l10n.dev/ws/translation-glossary.

Balance note: When --glossary is enabled, your balance is debited for the full source content upfront — even when --update is on. When disabled (default), a temporary internal glossary is generated automatically at no extra cost only for large files that exceed the AI chunk size.

Manual Glossary Override (`glossary`)

Supply your own term mappings via glossary in TranslationConfig (programmatic / batch config):

json

{
  "sourceFile": "./locales/en.json",
  "targetLanguages": ["de"],
  "glossary": [
    { "sourceTerm": "Settings", "targetTerm": "Einstellungen" },
    { "sourceTerm": "bank", "targetTerm": "Bank", "context": "financial institution" }
  ]
}

Omit or null: use the active saved glossary for this language pair
Empty array []: disable glossary entirely for this request
One or more entries: replace the active glossary for this request only

Terminology

Use terminology to enforce consistent terms across translations. List synonyms that should be replaced by the preferred term:

json

{
  "sourceFile": "./locales/en.json",
  "targetLanguages": ["de", "fr"],
  "terminology": [
    { "term": "Settings", "synonyms": ["Preferences", "Options"] },
    { "term": "Dashboard" }
  ]
}

Linguistic Instructions

Use instruction to set a Linguistic Instruction, it let you guide AI, for example:

📝 "Use formal tone"
📝 "Do not translate product names"
📝 "Use active voice"

Unlike glossaries that control specific terms, Linguistic Instructions control the overall style, tone, and translation behavior. Combined with AI Glossaries, they give much more control over localization quality and brand consistency.

bash

npx ai-l10n translate ./locales/en.json --languages de,fr --instruction "Use formal tone"

If not set it applies saved active linguistic Instruction.
Manage your saved linguistic Instructions at l10n.dev/ws/linguistic-instructions.

Managing Glossaries via CLI

Use the glossary command group to manage your translation glossaries directly from the terminal.

Glossary commands

bash

# List all glossaries
npx ai-l10n glossary list

# Create a glossary (active by default)
npx ai-l10n glossary create --source en --target de --name "My German Glossary"

# Show glossary details
npx ai-l10n glossary get 1

# Activate or rename a glossary
npx ai-l10n glossary update 1 --activate
npx ai-l10n glossary update 1 --name "Updated Name" --deactivate

# Delete a glossary (and all its entries)
npx ai-l10n glossary delete 1

Glossary entry commands

bash

# List all term mappings in a glossary
npx ai-l10n glossary entries 1

# Add a term mapping
npx ai-l10n glossary add-entry 1 --source "settings" --target "Einstellungen"
npx ai-l10n glossary add-entry 1 --source "bank" --target "Bank" --context "financial institution"

# Update a term mapping
npx ai-l10n glossary update-entry 1 42 --source "settings" --target "Einstellungen"

# Remove a term mapping
npx ai-l10n glossary delete-entry 1 42

Managing Linguistic Instructions via CLI

Use the instruction command group to manage linguistic instructions.

bash

# List all instructions
npx ai-l10n instruction list

# Create an instruction (active by default)
npx ai-l10n instruction create --source en --target de --text "Use formal tone (Sie, not du)"

# Show instruction details
npx ai-l10n instruction get 1

# Update an instruction
npx ai-l10n instruction update 1 --text "Use formal tone" --activate

# Delete an instruction
npx ai-l10n instruction delete 1

Language Support

l10n.dev supports 165 languages with varying proficiency levels:

Strong (12 languages): English, Spanish, French, German, Chinese, Russian, Portuguese, Italian, Japanese, Korean, Arabic, Hindi
High (53 languages): Most European and Asian languages including Dutch, Swedish, Polish, Turkish, Vietnamese, Thai, and more
Moderate (100 languages): Wide range of world languages

Language Codes

Use standard language codes (BCP-47 with optional script and region):

Simple: es, fr, de, ja, zh
With region: en-US, en-GB, pt-BR, zh-CN
With script: zh-Hans, zh-Hant
Full format: zh-Hans-CN

For ARB files, use underscores: en_US, zh_Hans_CN

Troubleshooting

API Key Issues

bash

# Check if API key is configured
npx ai-l10n config

# Set new API key
npx ai-l10n config --api-key YOUR_API_KEY

# Or use environment variable
export L10N_API_KEY=your_api_key_here

No Languages Detected

Auto-detection covers language-code folders (locales/en/common.json), language-code file names (locales/en.json, app_en.arb) and language codes inside file names (locales/emails.en.json). If your file names embed the code differently, describe the pattern:

bash

npx ai-l10n translate ./locales/emails.en.json \
  --language-regex "^emails\.(?<language>[\w-]+)\.json$"

Otherwise, specify languages explicitly:

bash

npx ai-l10n translate ./locales/en.json --languages es,fr,de

Insufficient Balance

Purchase more characters at l10n.dev/#pricing

VS Code Extension - Translate directly in VS Code

Support

📧 Email: support@l10n.dev
🐛 Issues: GitHub Issues
📚 API Documentation: api.l10n.dev/doc
🌐 Website: l10n.dev

Pricing

Free Characters: 10,000 characters free every month
Pay-as-you-go: Affordable character-based pricing with no subscription required
Current Pricing: Visit l10n.dev/#pricing for up-to-date rates

Privacy & Security

Secure API Keys: Stored securely in your home directory (~/.ai-l10n/config.json) or via environment variables
No Data Storage: Source code and translations are not stored on our servers beyond processing time
Encrypted Communication: All communication with l10n.dev API uses HTTPS encryption
Privacy First: Built by developers for developers with privacy, reliability, and quality as top priorities

💡 Tip for Large-Files Translation:

This npm package translates files in real-time via the Translate API and does not store your translations on our servers. For very large files, translation may take several minutes.

On the I18N File Translation page, you can:

Securely create translation jobs for batch processing

Set custom terminology for consistent translations

Monitor progress in real-time

Download files when complete with full control (delete anytime)

Important: Working with Arrays in JSON

⚠️ When using "Translate Only New Strings": If your JSON contains arrays (not just objects), ensure array indexes in your target file match those in the source file. When adding new strings, always append them to the end of the array.

Example:

json

// ✅ CORRECT: New items added at the end
// source.json
["Apple", "Banana", "Orange"]

// target.json (existing)
["Manzana", "Plátano"]

// After translation (new item appended)
["Manzana", "Plátano", "Naranja"]

// ❌ INCORRECT: Items inserted in the middle
// This will cause misalignment!
["Apple", "Cherry", "Banana", "Orange"]

For object-based JSON structures (recommended for i18n), this is not a concern as translations are matched by key names.

License

MIT

What it does

What it costs

ai-l10n

Features

Installation

For CLI + Programmatic (SDK)

For AI Agents (MCP Server)

For SDK Only

Getting Started

1. Get Your API Key

2. Configure API Key

3. Translate Your Files

Basic Translation

Advanced Options

Batch Translation

Configuration Management

Programmatic Usage

NPM Scripts Integration

CI/CD Integration

GitHub Actions

GitLab CI

Jenkins

Project Structure

Folder-Based Structure

File-Based Structure (JSON)

File-Based Structure (Flutter ARB)

Language Code Inside the File Name

Configuration Options

Content Filtering

Translation Glossary

AI Glossary Generation (--glossary / generateGlossary)

Manual Glossary Override (glossary)

Terminology

Linguistic Instructions

Managing Glossaries via CLI

Glossary commands

Glossary entry commands

Managing Linguistic Instructions via CLI

Language Support

Language Codes

Troubleshooting

API Key Issues

No Languages Detected

Insufficient Balance

Related Projects

Support

Pricing

Privacy & Security

Important: Working with Arrays in JSON

License

Credits

Similar modules

AI Glossary Generation (`--glossary` / `generateGlossary`)

Manual Glossary Override (`glossary`)