[posted in before 1900 cause the PoD would definitely have to be that far back]
What sort of scenario might see Germany and Russia fighting on the same side vs. Austria-Hungary, the Ottomans, France, and Britain?
I don't know much about that era of history, but seems to me that Russia and Germany have every reason to work together, given their mutual interests in challenging Britain either in Asia or on the seas. Britain and France had previously defend the Ottomans, and the Austrians and Ottomans both could have strong interests in preserving a Balkan status quo.