"Right" and "Left wing" is modernist terminology, and the revolution, as the shapeshifter that it is by nature, has expressed itself in the various doctrines that are ascribed to both terms. How is one to fight against the revolution by adopting it's language?
Liberalism, communism, fascism, national socialism etc. all share the same core of satanic doctrine, which is the subversion of the natural and supernatural order willed by God, and this is exactly what the revolution is by definition.
Also, when Churchmen spoke of nationalism in the past, they meant the poisonous flower which sprung from the cæsaro-papist seed which was already planted in olden Greco-Roman days, watered by men such as Barbarossa and which burst forth in the political systems of more recent times. The Church remembers how she has suffered by the germ of nationalism arrogating rights to the nation which it does not have. Verily, St. Albert of Louvain earned his crown of martyrdom through it's persecutions!
The real duty stemming from natural law to protect and contribute to the welfare of one's kindred and nation is not what nationalism is, and should therefore not be labelled as such. What nationalism is, is the attempt to make all things, including religion, the footstool of the nation.
The politics of St. Louis and of the vierge guerrière, St. Joan of Arc, divine politics, are the only ones to be aimed for by Catholics. Anything less is to be rejected. Christendom, and Christendom alone can liberate society from the multiple-headed beast which is the revolt against God, and all the consequences of it, which includes social/economical disorder.