BARCELONA is booming, the hotels full and taxis hard to find. The political conversation in Catalonia, one of Spain’s largest and richest regions, is about the everyday issues of housing, airport expansion and immigration. The local administration is waging an international campaign to promote Catalan gastronomy on the strength of more than 50 Michelin-starred restaurants in the region. Some of the 4,000 businesses that moved their domicile to other parts of Spain are trickling back. It is all a far cry from 2017, when a separatist Catalan government plunged Spain into turmoil with an unconstitutional referendum on secession and a unilateral declaration of independence, followed by the jailing of nine of its leaders.