The German competition law may also apply to foreign companies: when a company advertises with the domain name .de, German competition law applies.
The fact that a legal entity as a Swiss company has its headquarters in Switzerland is irrelevant, as confirmed by the German Supreme Court. The German legal system is always used when the content of advertising messages is directed to a German audience. Because a Swiss business uses a domain with the extension .de, it is clear that the statements were addressed to a German audience and the customer acquisition will take place in Germany as well. Thus, it is a subject to the German competition law.
Source: Berlin Court of Appeal, ruling Az 5U 20/14 from 27.11.12.