Luhmann was translated into English late, beginning only in 1979.

Evidence

The publication of the English versions of Trust and Power in 1979 was the very first time that any of Luhmann’s books had appeared in English. A Sociological Theory of Law was to follow five years later, and Love as Passion in 1986. His major theoretical work Social Systems was published in the 1990s, as well as several other of his many books and articles. These publications reflect an initial burst of interest among English-speaking sociologists in Luhmann’s new scientific, ideology-free sociology. — Niklas Luhmann, Trust and Power, 33