Using recipes from around the world can be frustrating in Germany. I've found a few things that might be helpful so you don't have to recreate the wheel (and so that I remember!).
American Brown Sugar - American brown sugar is different from brown sugar else where. In the UK, Sri Lanka, and Germany brown sugar is unrefined sugar and it usually has large crystals. In the USA brown sugar comes in a variety of forms, such as, light brown, dark brown, etc. This sugar is made from refined sugar and then has the molasses added back into it. Hence, the fine crystals and the moistness. I make "American brown sugar" in Germany by adding molasses (goldsaft seems to work fine) to regular sugar. You can mix it in until you get the right colour and then store it (or you can just add a bit of goldsaft to the batter).
Baking soda - supposedly the same as Natron although I have not tried Natron. Arm and hammer baking soda is available at some of the larger Real's (there is one opposite the IKEA in Dortmund).
Appa Soda - same as baking soda
Bicarbonate of Soda - same as baking soda
All purpose flour - not freely available in Germany. All purpose flour is a mixture of many different flours. German flour is pure wheat flour. In the USA pure wheat flour it is commonly known as pastry flour or cake flour.