Or, perhaps, there's an in-game option to do so, but I wouldn't know. I'm not big into IT, but I've been learning German for over 5 years and I'm fairly fluent at it now.
Well, where-ever you end up looking, try looking for anything called 'Einstellungen' for 'options', or 'Sprachen' for 'languages'. 'German' will be known as 'Deutsch' and English will be known as 'Englisch' (not much difference there).