Final answer:
In the 18th century, Italian opera was least popular in Paris as the Parisian audiences and cultural scene favored their own French operatic traditions over Italian ones.
Step-by-step explanation:
Generally speaking, during the eighteenth-century, Italian opera was relatively less popular in Paris compared to other major cultural centers of Europe such as London, Vienna, and Berlin. Paris had its own flourishing tradition of French opera, which often overshadowed the Italian opera during this period. The Italian genre was highly favored in places like London and Vienna, and to some extent, Berlin, where the courts and public had a marked preference for the Italian style of music and opera performance.
By comparison, Parisian audiences were more inclined towards their native French operatic traditions, epitomized by composers such as Jean-Baptiste Lully and later Christoph Willibald Gluck, who although was of German descent, his work is often associated with the French operatic tradition. The city of Paris was also famously particular about French culture and language, which contributed to the preference for French operas. This nationalistic preference meant that Italian operas would take a backseat to the French productions.