You have to access the built-in settings because I can't find anything related to language switching and general availability of the application. Start the software and then go through the menus until you can see the actual name of the language. It's a matter of a few seconds searching.
There could be a possibility as well, that German to be the only language supported by the software and you should contact the seller to ask for an English version.
I've searched on Google Search, but couldn't find anything available.