This thread is resolved. Here is a description of the problem and solution.
Problem: I want the invoices and packing slips to be translated in the language the order is placed in.
Solution: This is not working with the "Invoices and Packing Slips" free version. In another support ticket, the author told it's working with the professional version of this plugin. Please see the plugin description for further details.
Best Marcel Relevant Documentation: https://wpml.org/forums/topic/woocommerce-pdf-invoices-packing-slips-3-strings-not-available/page/2/
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