Both of Patchouli-sama's names are English, which implies that she speaks it.
Her friend Remilia, is Eastern European, and the maid, Sakuya, is known to have originally had another name, which implies that most of the SDM are racially superior Europeans.
I wouldn't have a problem communicating with mai waifu because she speaks English like a civilised person should. Japanese is pretty poor at expressing modern concepts, and hopefully the Japs will abandon it they way that Europeans are getting rid of languages like Dutch, Norwegian, Danish, etc. and adopting the global language (English) in their place.