This multi-cultural environment led to many revolts by minority groups trying to secede from the kingdom; One of the most well-known examples is the nation of Neutral-Moresnet. Moresnetians had for a long time been a minority in many different countries all over the world. However, in Preussen-Nassau, there had always been particularly many of them: At its peak, their number made up 21% of the entire population! Nowadays though, their number has been reduced to only about 1%, due to a mass emigration of Moresnetians after the creation of Neutral-Moresnet as their own nation.
Another sizable majority, that currently makes up about 10% of Preussen-Nassau's population are the French. Especially in recent history, they have been one of the very few minorities that still seeks to establish an own nation-state. Riots and protests are not common though anyways.
The minorities in Preussen-Nassau have always enjoyed equal rights & privileges and still do so up to this day; The only significant change regarding their treatment are the language-policies:
In the early days of Preussen-Nassau, before the national identity of being a "Preussisch-Nassauer" had formed, the massive amount of different languages within the countries borders was deemed problematic by the country's parliament, the Generalstaaten. Translating each law into every single one of the languages had become too expensive for the very tight national budget at the time. Therefore, only the German language was given an official status and a law was passed that made it illegal for government officials to work in any other language. Soon, school classes had to be in German as well and for some time, it even became illegal to speak any other language than German at all, which led to the extinction of many minority languages.