Hi René,
I’m afraid we have no clue. 🤷🏻♀️
Maybe this article from WPML documentation will help you to solve your issue as it seems to answer to the same concern: MailChimp for WordPress Multilingual
Please note that this issue is related with the use of a third party plugin, not with the use of your theme. As theme authors, the installation, setting or debugging of third party plugins isn’t part of the support we will provide.
To go further, we invite you to ask for more help from the plugin authors and post your request on their support forums: WPML Support forum
We remain available for all support requests related with the use of your theme.
Regards,