Not so much an army, more a tower of Babel, one might think

From The Long Shadow: The Legacies of the Great War in the Twentieth Century by David Reynolds.  Page 7.

Before the war, some Croat and Slovene intellectuals within the Habsburg Empire had talked of sharing a common South Slav (Yugoslav) identity with the Serbs, but they were a minority. The striking point about 1914, however, was that imperial loyalties held firm. In the Habsburg campaign to crush Serbia in the autumn of 1914, many of the soldiers were of South Slav extraction. Notwithstanding occasional nationalist outbursts, for most of the war the Habsburg Army hung together and fought well, despite an ethnic diversity that seems ludicrous today. For every hundred men in the Imperial Army in 1914, there were on average 25 Germans, 18 Magyars, 13 Czechs, 11 Serbs and Croats, 9 Poles, 9 Ruthenes, 6 Romanians, 4 Slovaks, 2 Slovenes, and 2 Italians. The language of command was German, with a repertoire of eighty different orders, but officers were expected to know the Regimentssprache, the language or languages spoken by their men. Many units operated with two languages, some as many as five. Not so much an army, more a tower of Babel, one might think, yet this polyglot command hung together until 1918, when most soldiers effectively went on strike.