It is the same with Diesel, which can be capitalised or not. Do the words Reich and Kaiser have some specific historic value as they are distinguished from non-capitalised words such as halt, ozone, heroin, nickel, semester, etc?
Learn English – Why are the words Reich and Kaiser capitalised in English
capitalizationorthography
Best Answer
Firstly, it's not as homogeneous as you'd believe it: the New Oxford American Dictionary, for example, doesn't use the capital for kaiser unless it's an official title (see #2).
Secondly, titles typically become capitalized when they become part of a person’s name. So, it would be “the queen was not amused”, but “he said Queen Victoria was not amused”.
Thirdly, names of sovereign states (whether in the present or in the past) are usually capitalized too. So, you’d say “he has nostalgia for the Reich” (implicitly, “the Third Reich”) as you would say “Austria was then part of the Holy Roman Empire”.