A very useful collection of Habermas texts on line can be found at: http://www.helsinki.fi/~amkauppi/hablinks.html
It is no doubt rather harsh to link Jürgen Habermas with German nationalism, Habermas epitome of decent rationalist sort of Marxist sort of left-liberal German democrat. His thought repudiates all Nationalism in favour of cosmopolitan democratic procedures based on the ethics of discourse undistorted by the interests of power. He devotes himself to Constitutional Patriotism, which rests on loyalty to constitutional arrangements rather than loyalty to culture, ethnicity, race or religion.
But this becomes another form of German Nationalism? Who has supposedly provided an example of Constitutional Patriotism? The post-war Federal Republic of Germany of course.
Which nation reacted most strong against proto-totalitarian Jacobin Terror during the French Revolution, supposedly? Germany of course, though one might point out that Edmund Burke pointed out this aspect of the French Revolution before it had happened. Statist elements in Fichte and Hegel are overlooked by Habermas. What about the consequences of Marxist utopianism in politics: totalitarianism What about Marx's anti-semitism in On the Jewish Question? What about the nationalist element in the thought of liberal thinker and sociologist Max Weber? Though quite rightly, Weber would certainly think something is missing from the idea of Constitutional Patriotism,which rests on an ideal of passionless depersonalised discourse. If we look at a great German liberal of that time, Wilhelm Von Humboldt, we find a regret for the passing of constant war in human civilisation and a strong belief in the 'Nation' as the source of laws, unified by the interplay of constant dialogue.
Humboldt has some leanings towards militaristic nationalism, along with the limited state. His emphasis on dialogue provides a source for Habermas' discourse ethics and democracy of deliberation. No mention of how that works out in conjunction with Humboldt. Where is Marx, who turns a Humboldtian emphasis on freedom through dialogue into a socialism/communism where individuals flourish in their freedom from the state?
Habermas overlooks Naziism and its place in German history while defining Germany as the home land of constitutional patriotism. Patriotism requires more than loyalty to a constitution. I do not suppose that Habermas overlooks the complaints mentioned above, but he has no answer other than an idealised public sphere where individuals keep debating detached from anything which makes them individual.
Of course there is much to admire in Habermas' thought and in German constitutionalism, but we need material interests and personal perspective in an adequate theory. We certainly do not want a universalisation to German politics, mirroring the Jacobin universalism which Habernas criticises.