The German Market plugin requires the WooCommerce Tax API, which is only available starting with WC 3.7. In Germany, there are actually just three choices: Either you use German Market, you use Germanized for WooCommerce / WooCommerce Germanized, or you use an actual professional, ie. a lawyer specialized in online law, which is of corpse much more expensive vs. prepared text + a quick checkup.
My guess is, that WooCommerce, as most WordPress plugins, was never really meant / tested for international use. Hence all the issues with eg. Table-based shipping calculations. And thus, also the issues with a non-existing Tax Calculation API / class framework. Just think of: The US with its semi-non required VAT system vs. the REQUIRED VAT in Europe and related countries (eg. the Commonwealth of Nations).
Its not so much about GDPR, its mostly about required = mandatory taxes. Eg. here in Germany, the current mandatory (!) VAT on regular products and services is 19%, and for nurturous food (in theory) and books and several other “essential” things its 7% (eg. the Deutsche Bahn got their VAT reduced by decree during the current CoVid-19 crisis, from “service” 19% down to “essential” 7%).
No, I’m not gonna give it a try, because I already did. It doesnt work.
Thats why I’m using WC 3.7.x. The Tax API is differently implemented in 3.7, and that is what one of the most important plugins for staying “safe” in the German (and, to some extent, European) market uses. I have not yet tried 3.8, because one cannot “just” upgrade WooCommerce and think everything will be alright - most of the time it wont.
Also, it is important to point out that the most current version of German Market, ie. 4.0, won’t work with ClassicPress or WP 4.9.x anymore (the latest that still works is 22.214.171.124). But its rival, Germanized for WooCommerce, still does.
I’ve edited it. You have to remember: I’m German. We don’t learn much in history in school, despite the time from 1920 to 1945