Translation of PDF Documents not working properly

Hi there
I am using Woocommerce and the Plugin “WooCommerce PDF Invoices & Packing Slips” to generate PDF Invoices. My site is german (default) and translated to french as well.
In order to translate PDF invoices I added this filter to my functions.php:
add_filter( 'weglot_translate_pdf', '__return_true' )

While the translation of the documents works perfectly fine in french, however, if I want to view the Invoice in german, it displays me a blank PDF. I assume the filter somehow interferes with the plugin. If I remove the filter, the german PDF is generated and displayed properly.

I am asking you: Is there a way to only activate this filter when the current language is french? Or how would you resolve this issue?

Many thanks for your help!