I found out that I have to scan strings and plugins and choose texts for translation as described here: https://wpml.org/documentation/getting-started-guide/string-translation/finding-strings-that-dont-appear-on-the-string-translation-page/
The translation is done now.
I added a captcha to the form. In the free version it was working fine. In Pro version the chaptcha is not showing.
(example: https://borowski-glas.de/produkt/tawny-3/)
Please inform me if there is anything to know about your plugin concerning the regulations of the GDPR.
And: I thought I solved the problem with the short descriptions of the product variations but I did not. When I switch to a standard theme it does not help. Deactivating all other plugins also not. Only after deactivating Catalog Enquiry the short description of the variation is displayed.