I seem to remember the authors being Czech. This is also suggested by the fact that the Czech website is different from other language variations and gives a Prague address for mail orders. Maybe the developers are in Prague and sales go through Germany.
https://www.proficad.com/purchase.aspx#faq
Digital River GmbH Scheidtweilerstr. 4 50933 Cologne Germany Tax ID Number (Germany): 217/5722/1080 VAT-ID: DE194149069