Hence, any analogy between the situation of Catalunya and the reactionary Lega Nord campaign in Lombardy and Veneto is, in the best case, an expression of pure ignorance and, in the worst, a chauvinist assault against the Catalan people.
First, the Catalans constitute a nation. Even Spain’s anti-democratic post-Francoist constitution of 1978 recognizes the existence of the Catalans and the Basques as nationalities. The inhabitants of Lombardy and Veneto, while possessing a specific regional and cultural identity, do not constitute a nation separate from the Italian nation. Leaving aside the leaders of the extreme right-wing and racist Lega Nord, no one in Italy would characterize the people of Lombardy and Veneto as separate “nationalities.”
Secondly, the Catalan (as well as the Basque) minorities have been historically oppressed and underprivileged nations. For centuries they have been discriminated against by the Castilian-dominated ruling class of the Spain state and its centralist bureaucratic apparatus. Their language and their culture have been suppressed and historic Catalan leaders, like Lluís Companys, have been murdered by Madrid.
This is why Marxists, as Trotsky already elaborated in his writings on Spain in the 1930s, have historically recognized the duty to defend the Catalan’s national and democratic right against the imperialist Spanish State.
“But what has been said does not at all diminish the progressive revolutionary-democratic character of the Catalonian national struggle—against the Spanish great-power spirit, bourgeois imperialism and bureaucratic centralism. It must not be left out of sight for a minute that Spain as a whole and Catalonia in particular are at present governed not by Catalonian national-democrats but by Spanish bourgeois-imperialists in alliance with the landowners, old bureaucrats in general, with the support of the Spanish national-socialists. This whole fraternity stands, on the one hand, for the continued subjugation of the Spanish colonies and, on the other—for the maximum bureaucratic centralization of Spain itself, that is, for the suppression by the Spanish bourgeoisie of the Catalonians, the Basques, etc. At the given stage of developments, with the given combination of class forces, Catalonian nationalism is a progressive-revolutionary factor. Spanish nationalism is a reactionary-imperialist factor. The Spanish Communist who does not understand this difference, ignores it, does not advance it to the front rank, but on the contrary, covers up its significance, risks becoming an unconscious agent of the Spanish bourgeoisie and is lost to the cause of the proletarian revolution.” 
Nothing like this can be said about the Italian provinces Lombardy and Veneto. The North has always dominated the country since the foundation of the modern Italian nation-state in 1870 and if there is something like a historically discriminated part of Italy, it is the South. The Italian Marxist Antonio Gramsci even characterized Italy‘s South – the Mezzogiorno – and its islands like Sicily and Sardinia as “internal colonies”. In his famous study on “The Southern Question”, he elaborates on the Italian communists’ statement written in 1920: “The Northern bourgeoisie has subjugated the South of Italy and the Islands, and reduced them to exploitable colonies.” 
 Leon Trotsky: The Progressive Character of Catalan Nationalism (1931), in: Leon Trotsky: The Spanish Revolution (1931-39), Pathfinder Press, New York 1973, p. 110, https://www.marxists.org/archive/trotsky/1931/spain/spain03.htm
 On this see, e.g., Antonio Gramsci: Some Aspects of the Southern Question (1926), in: Antonio Gramsci. Selections from Political Writings 1921-1926, Lawrence and Wishart Ltd, London 1978, pp. 441-462