Nation State as defined by Scruton. A body of people existing through time, in a specific geographic area, under a government they (broadly) accept.
Then ancient Egypt was a nation-state. This is completely anachronistic as the idea of nation-state dates from 19th-century Europe.
100 years ago, the Austro-Hungarian Empire was a nation-state. Now it's been divided in 6 countries with bits belonging to yet other countries. But would you say that the Czech Republic or Croatia are not nation-states ? Or was it Austro-Hungary that wasn't one. If it wasn't one, what makes you think that Germany or Italy or Spain are more culturally or genetically uniform that Austro-Hungary ?
If genetics and regional culture define the nation-state, then nation-states should be small, about the size of modern Austria, or Bavaria, or Flanders, or Catalonia, or Wales...
If the common language is what matters, then France, Germany, Italy or Austro-Hungary were not nation-states to start with, because people used to speak many languages or unintelligible dialects. 100 years ago, over 90% of the people in the southern half of France could not speak or understand Parisian French and did not identify with France as a nation. Same in Italy. How many Austro-Hungarian spoke German or Hungarian or both ?
It doesn't matter how long look at it, big countries like France or Germany cannot be logically considered as nation-state. This was all late 19th-century propaganda to enrol people in the army.
Even a small country like Belgium isn't a nation-state because it has two distinct linguistic/cultural groups that do not see each other as one nation but two under a central government.
Add to this the modern population movement. People marry outside their country borders, work abroad, settle abroad... There are about 10% of "foreigners" (people born and raised in another country, even if later naturalised) in most Western European countries nowadays. In Switzerland it is over 20%.
Then it is becoming commonplace in Europe for people to speak several languages. So even being united under a common language doesn't mean much nowadays. Culture is also increasingly globalised. There is less difference in lifestyle between Cologne and Bordeaux nowadays than there was between Cologne and Munich 100 years ago. The difference is even more flagrant when you compare life in Europe and Japan 150 years ago and now. We passed from 2 completely separate world to places where you could have pretty much the same lifestyle, values and hobbies once the language barrier is removed.
So at what level do you place the nation-state in modern society ? Does it still exist ? Are all countries nation-states for you ? If not give examples, please.