App Store Localizer

On a Mac, install it with Homebrew in the Terminal app:

brew install fastlane
fastlane --version

An API key lets fastlane sign in without two-factor authentication prompts.

1. Open App Store Connect, go to Users and Access, Integrations, App Store Connect API.
2. Create a key with the App Manager role and download the .p8 file. It can be downloaded only once, so keep it safe.
3. Note the Key ID and the Issuer ID shown on the same page.

Next to your fastlane folder, create api_key.json:

{
  "key_id": "YOUR_KEY_ID",
  "issuer_id": "YOUR_ISSUER_ID",
  "key": "-----BEGIN PRIVATE KEY-----\nKEY_CONTENT\n-----END PRIVATE KEY-----",
  "in_house": false
}

The key must be on one line with \n instead of line breaks. This command prints it in that form:

awk 'NF {printf "%s\\n", $0}' ~/Downloads/AuthKey_XXXX.p8

Unzip the downloaded file into the fastlane folder of your project:

your-project/
├── api_key.json
└── fastlane/
    └── metadata/
        ├── en-US/   (name.txt, subtitle.txt, description.txt)
        ├── de-DE/
        └── pl/

Folder names are App Store locale codes such as en-US, de-DE or pl. Keep them as they are, fastlane rejects other names.

App Store Connect needs a version in the Prepare for Submission state. Then run, with the Bundle ID of your app:

cd ~/path/to/your-project
fastlane deliver \
  --api_key_path api_key.json \
  --app_identifier com.example.app \
  --skip_binary_upload \
  --skip_screenshots

• For a macOS app, add --platform osx.
• fastlane shows a preview in the browser and asks for confirmation. It only updates the texts, nothing is submitted for review.
• To back up the current texts first, run this in an empty folder: fastlane deliver download_metadata --api_key_path api_key.json --app_identifier com.example.app

An error like Could not find app or team_id for nil means fastlane signed in but could not find an app with this Bundle ID. Check that:

• the command has your real Bundle ID, not com.example.app. Copy it from App Store Connect, App Information, Bundle ID. It is case-sensitive;
• the API key comes from the same team as the app, if you have access to several developer accounts;
• the app already exists in App Store Connect.

The download_metadata command above is a safe test: it only downloads texts, so if it works, the Bundle ID and the key are right.