Google Play Localizer

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

brew install fastlane
fastlane --version

fastlane signs in to Google Play with a Google Cloud service account:

1. Open the Google Cloud console, select or create a project and enable the Google Play Android Developer API.
2. Go to IAM & Admin, Service accounts, create a service account, open it, go to Keys and create a JSON key. Save the file as service-account.json next to your fastlane folder.
3. In Play Console, go to Users and permissions, invite the email address of the service account and allow Edit store listing, pricing and distribution for your app.

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

your-project/
├── service-account.json
└── fastlane/
    └── metadata/
        └── android/
            ├── en-US/   (title.txt, short_description.txt, full_description.txt)
            ├── de-DE/
            └── pl-PL/

Folder names are Google Play language codes such as en-US, de-DE or pl-PL. Keep them as they are, Google Play rejects other names.

Run, with the package name of your app:

cd ~/path/to/your-project
fastlane supply \
  --package_name com.example.app \
  --json_key service-account.json \
  --skip_upload_apk \
  --skip_upload_aab \
  --skip_upload_changelogs \
  --skip_upload_images \
  --skip_upload_screenshots

• Only the texts are uploaded, no app bundle or release. The changes are published to your store listing, and Google may review them first.
• To back up the current texts first, run this in an empty folder: fastlane supply init --package_name com.example.app --json_key service-account.json

This error means fastlane signed in, but the service account cannot edit the app. Check that:

• the command has your real package name, not com.example.app;
• the service account is invited in Play Console with access to this app. A new invitation can take a few minutes to work;
• the Google Play Android Developer API is enabled in the Google Cloud project of the service account.

The supply init command above is a safe test: it only downloads texts, so if it works, the package name and the key are right.