Since the version 4.4.4 Flexible PDF Invoices support WPML and Polylang.
For some time now we have been boasting that we have been adapting the WordPressinvoices and WooCommerce Invoices to European law standards. We are making changes so that you can automatically invoice customers from around the world and save your time.
Flexible PDF Invoices support WPML
We are proud of recent implementations, but we realize that all these changes would not be sufficient if invoices could be issued in one language only.
We know from you how important the functionality is to be able to sell and invoice in your customers' languages. That is why since the ... we have implemented changes that make WordPress PDF Invoices support WPML and Polylang. With this change, you can issue all types of documents supported by the plugin - invoices, corrections, MOSS invoices - in the languages you sell in your WooCommerce shop.
What translations are supported by the WordPress Invoices plugin?
Currently the plugin supports English, Polish and Dutch. But we hope because of these changes the number of languages supported by Invoices will grow up. If you want to become a WordPress Invoice translator, you can start doing it here. Once the translation is accepted, you will be added to the plugin description as the author of the translation.