This is the Invoices for WooCommerce Github repository. Browse the source code, add your own issues and keep track of development.
Support can take place on the plugins support forum on WordPress.org, where I will try to respond as soon as possible.
Use the issue tracker for enhancement requests or report problems with the source code. Have some fancy code? Fork the repository and send a pull request.
For adding your translation files the code, add your translation and send a pull request. Read the WordPress Codex to learn how to translate a plugin.
The GitHub App for Mac and Windows helps managing your forked repository.