The issue of the mail not being sent, comes from that this shortcode creates an issue:
<p><?php printf( _e( 'Ready to get started?', 'woocommerce' ); ?></p>
The printf doesn't work properly.
I've changed it to:
<p><?php esc_html_e( 'Ready to get started?', 'woocommerce' ); ?></p>
To see if we can proceed. And this keeps the template working. I've managed to do an order in the system. And you can see both orders in the mail logger now.
For some reason, this shows that it works now actually. Hooray. There is one small translation bit in the english version that seems to be dutch.
The word on the english mail: "Besteloverzicht" should be 'Order summary'.
I think I can slowly proceed to reimplement the code and hopefully identify this way, where it goes wrong.
Both PHP functions you have mentioned are ok to use. So I think it is ok if you use esc_html_e.
Also I suggest that you start over and move the base file to the child theme without any changes and test and make sure the email language is correct without any custom code.
If it is then you can start slowely add the custom codes.
But if it is not, then you need to check for the problems in WPML > String Translation. Try to make sure that you also check the "Also show trasnlations" checkbox in the search section and search for the string tthat is not ok.
If you find one and you see that the flag shown in string trasnlation is not corresponding with the actiual string, please do as follows:
