I dream of an official Prussian civ and an Austro-Hungarian civ in Age of Empires III: Definitive Edition in DLC 
Prussian civ
Prussians civ would be a civilization of infantry (lots of ranged units) and industry (building Grube - this building is being built on a mine providing an unlimited source of coins, but slowly and construction limit. Only Miners (speaking in Silesian) could work there - they would be trained in the Mine or available in Home City cards (at the beginning of the game the Prussians would have one Miner). They have a unique Outpost - Grenzposten in which can train Landwehr
The only archaic unit that the Prussians would have could be the Teutonic Knight (a cavalry unit with a lance that can dismount and fight as a two-handed swordsman), which would be a reference to the Teutonic Order from which Prussia was founded.
Austria-Hungary civ
Austria-Hungary would be a civilization of a weak but numerous infantry that could flood enemies with their numbers (UU Austro-Hungarian infantry would occupy a small number of the population). Austria-Hungarian civ would benefit from good cavalry, cheap Taverns and a unique Festung building (connection of the Barrack with the Stable. Unlike Fort and Blockhouse, it doesn’t defend.
Austria-Hungary, due to multi-ethnicity, would have units that speak several languages, e.g:
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Pandur - Croatian language
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Hungarian Hussar - Hungarian language
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Hajduk (trained in the Barracks or in the Tavern as a mercenary) - Bosnian or Serbian language
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War Wagon (in my opinion it should be renamed to the Hussite Wagon. It would be a unit available only with Home City cards) - Czech language
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A nice option would be a unique Settler - Gorals. It would be a Shepherd’s ax armed unit and would be slightly more durable than a regular Settler. It would have more powerful melee attacks, but it would not be able to fight at a distance. This unit could train sheep. This unit would speak the Slovak language
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The other units would speak German