The Institute fully Americanized after the mid-1930s, publishing only in English

Evidence

In moving westward to California, Horkheimer and Adorno gave symbolic confirmation of the Institut’s increased distance from its European origins. In February, 1940, while still in New York, Horkheimer, Pollock, Marcuse, and Lowenthal had taken out naturalization papers. By the end of the war almost all the Institut members had become American citizens. The end of the Zeitschrift meant the beginning of a new English-speaking audience for the Institut. Starting with Punishment and Social Structure in 1939, all the Institut’s published work appeared in its adopted language. — Martin Jay, The Dialectical Imagination, 530