But it is an important point here, because this is one of the main things nationalism is blamed for. When you come from small states , kingdoms and principalities a nation based on language to me seems not as an idea of segregation. Of course all the others that don't belong to that nation are somehow segregated (not saying that this must be any kind of bad in terms of peace and freedom). If Europe was a nation you would make a statement still pointing out that the rest of the world was segregated. Even human identity works by defining who you are and who you are not, cultural and subcultural membership the same. Nothing bad about it, as long as your own interests and views don't affect others rights and personal freedom. So for you possibly there is only socialism one world utopia left to call out for. To me it makes no difference if you call out for a world of nations living in peace,of course this utopian also.

In 1848 it was the most integrating way that was possible at this time for the germans. And the idea never meant "segregation". It was students proclaiming their new ideas just like the 68' movement. Of course we have seen excessive form of nationalism, this does not make it bad in general.
You can say the same of any other state form. It's the people themselves that must become free and independent, self-conscious, so they can't be misleaded by any abuse of a system whether it is nationalistic or socialistic or whatever.