It's Deutsche Schaeferhund, so the translation to GSD is accurate. Who knows why it caught on? But that's what it's always been called.
Well, except for that period of time after World War 2 when the breed was rechristened 'Alsatian' by the AKC.
At any rate, German Shepherd Dog is the official name of the breed as used by the AKC, and every other English speaking dog registry that I am aware of.