On the site it says:

Hierbei handelt es sich nicht um die originalen Versionen von osticket.com, sondern um modifizierte, übersetzte Versionen.

In English it means:

These are not the original versions from osticket.com, instead it's a modified, translated (to German) version.

So based on that it's clearly stated that it's NOT an official osticket and I wouldn't use it even though support is offered and it's in German, which is usually great for a German guy like me, but since we only use OS and software in English at my company I prefer the original osticket and always confused with German OS or software (even at private devices like my phone from which I type now)

@[deleted] answer is pretty right on the money.  Let me further add that they (osticket.com.de) is not affiliate in any way with osticket.com other than they translate the software released here into German and try to provide support for it.  We also do not provide support for their product.