TypeScript

AI translation for TypeScript localization files with Lingo.dev CLI

What is TypeScript localization?

TypeScript localization files use TypeScript/JavaScript object syntax to store translation strings. They are commonly used in modern web applications for type-safe internationalization.

For example:

const messages = {
  navigation: {
    home: "Home",
    about: "About Us",
    contact: "Contact Us"
  },

  forms: {
    title: "Contact Form",
    nameLabel: "Your Name",
    submitButton: "Send Message"
  },
};

export default messages;

What is Lingo.dev CLI?

Lingo.dev CLI is a free, open-source CLI for translating apps and content with AI. It's designed to replace traditional translation management software while integrating with existing pipelines.

To learn more, see Overview.

About this guide

This guide explains how to translate TypeScript localization files with Lingo.dev CLI.

You'll learn how to:

  • Create a project from scratch
  • Configure a translation pipeline
  • Generate translations with AI

Prerequisites

To use Lingo.dev CLI, ensure that Node.js v18+ is installed:

❯ node -v
v22.17.0

Step 1. Set up a project

In your project's directory, create an i18n.json file:

{
  "$schema": "https://lingo.dev/schema/i18n.json",
  "version": "1.10",
  "locale": {
    "source": "en",
    "targets": ["es"]
  },
  "buckets": {}
}

This file defines the behavior of the translation pipeline, including what languages to translate between and where the localizable content exists on the file system.

To learn more about the available properties, see i18n.json.

Step 2. Configure the source locale

The source locale is the original language and region that your content was written in. To configure the source locale, set the locale.source property in the i18n.json file:

{
  "$schema": "https://lingo.dev/schema/i18n.json",
  "version": "1.10",
  "locale": {
    "source": "en",
    "targets": ["es"]
  },
  "buckets": {}
}

The source locale must be provided as a BCP 47 language tag.

For the complete list of the locale codes that Lingo.dev CLI supports, see Supported locale codes.

Step 3. Configure the target locales

The target locales are the languages and regions you want to translate your content into. To configure the target locales, set the locale.targets property in the i18n.json file:

{
  "$schema": "https://lingo.dev/schema/i18n.json",
  "version": "1.10",
  "locale": {
    "source": "en",
    "targets": ["es"]
  },
  "buckets": {}
}

Step 4. Create the source content

If you haven't already, create one or more TypeScript localization files that contain the content to be translated. These files must be located at a path that includes the source locale somewhere in the path (e.g., as a directory name like en/ or as part of the filename like messages.en.ts).

Step 5. Create a bucket

  1. In the i18n.json file, add a "typescript" object to the buckets object:

    {
  "$schema": "https://lingo.dev/schema/i18n.json",
  "version": "1.10",
  "locale": {
    "source": "en",
    "targets": ["es"]
  },
  "buckets": {
    "typescript": {}
  }
}

  2. In the "typescript" object, define an array of one or more include patterns:

    {
  "$schema": "https://lingo.dev/schema/i18n.json",
  "version": "1.10",
  "locale": {
    "source": "en",
    "targets": ["es"]
  },
  "buckets": {
    "typescript": {
      "include": ["./[locale]/example.ts"]
    }
  }
}

    These patterns define which files to translate.

    The patterns themselves:

    • must contain [locale] as a placeholder for the configured locale
    • can point to file paths (e.g., "[locale]/messages.ts")
    • can use asterisks as wildcard placeholders (e.g., "[locale]/*.ts")

    Recursive glob patterns (e.g., **/*.ts) are not supported.

Step 6. Configure an LLM

Lingo.dev CLI uses large language models (LLMs) to translate content with AI. To use one of these models, you need an API key from a supported provider.

To get up and running as quickly as possible, we recommend using Lingo.dev Engine — our own, hosted platform that offers 10,000 tokens of free, monthly usage:

  1. Sign up for a Lingo.dev account.

  2. Run the following command:

    npx lingo.dev@latest login

    This will open your default browser and ask you to authenticte.

  3. Follow the prompts.

Step 7. Generate the translations

In the directory that contains the i18n.json file, run the following command:

npx lingo.dev@latest run

This command:

  1. Reads the i18n.json file.
  2. Finds the files that need to be translated.
  3. Extracts the translatable content from the files.
  4. Uses the configured LLM to translate the extracted content.
  5. Writes the translated content back to the file system.

The first time translations are generated, an i18n.lock file is created. This file keeps track of what content has been translated, preventing unnecessary retranslations on subsequent runs.

Example

en/example.ts

const messages = {
  navigation: {
    home: "Home",
    about: "About Us",
    contact: "Contact Us",
    services: "Our Services"
  },

  forms: {
    title: "Contact Form",
    nameLabel: "Your Name",
    emailLabel: "Email Address",
    messageLabel: "Your Message",
    submitButton: "Send Message",
    successMessage: "Thank you for your message!",
    locked_key_1: "This value is locked and should not be changed",
    ignored_key_1: "This value is ignored and should not be processed"
  },
};

export default messages;

es/example.ts

const messages = {
  navigation: {
    home: "Inicio",
    about: "Sobre Nosotros",
    contact: "Contáctanos",
    services: "Nuestros Servicios"
  },

  forms: {
    title: "Formulario de Contacto",
    nameLabel: "Tu Nombre",
    emailLabel: "Dirección de Correo Electrónico",
    messageLabel: "Tu Mensaje",
    submitButton: "Enviar Mensaje",
    successMessage: "¡Gracias por tu mensaje!",
    locked_key_1: "This value is locked and should not be changed",
  },
};

export default messages;

i18n.json

{
  "version": "1.10",
  "locale": {
    "source": "en",
    "targets": ["es"]
  },
  "buckets": {
    "typescript": {
      "include": ["./[locale]/example.ts"],
      "lockedKeys": ["locked_key_1"],
      "ignoredKeys": ["ignored_key_1"]
    }
  },
  "$schema": "https://lingo.dev/schema/i18n.json"
}

i18n.lock

version: 1
checksums:
  0cdc4f3ba34edc7f3ba4d996158306ad:
    navigation/home: 104a3db3b671c04e167eafbe21e57881
    navigation/about: 8f89131a66d4659be07cd5af2c7ea898
    navigation/contact: 2a75337dc9603915c4ec1d1905afb7b9
    navigation/services: 999f32026e64978cb3ec794a496b0bb8
    forms/title: ac85dea7c7f0bf1cd7d48cc1b4da3acc
    forms/nameLabel: 03c6ae7996d5841f743cd406b4eff72d
    forms/emailLabel: 0ee22bbbe989a0c61a18023407d12dc2
    forms/messageLabel: 1e460d0909502d0e94b9be562643af0d
    forms/submitButton: 487177489aafc9c0243c57ef3850a2d9
    forms/successMessage: a0a7aa980dffa31d4d194af718a917b3
    forms/locked_key_1: 73fc105de1aefc3f0a97d187a80cf0a4
    forms/ignored_key_1: d88a7aa6c5661ca901ee0f4cb51e3a0d