1) Kulturelle Verschiedenheit.

1904
One of the points most emphasized by Professor Boas on that occasion [the presidential address before the American Folklore Society] was the importance of the contents of the mind in determining cultural diversity in various environments. Whether one admits or denies the logical inferences from the argument advanced at that time, the truth of the proposition that the experience of the individual will determine, to a great extent, the action of the individual, and that the experience of the group will determine the action of the group, is obvious at a glance. Further, that in savage communities the collective experience is epitomized in the traditions of the community, is also evident.
Livingston Farrand: The significance of mythology and tradition, in: The Journal of American Folklore 17 (1904), S. 14-22, hier S. 21.

1913
Since the earliest times progress has been due in part to contact of one people with another and the resulting interchange of ideas. Infiltrations and invasions, peaceable or otherwise, have also brought changes. The evidence points to a diversity of human types as far back as the early Quaternary, but not to a corresponding cultural diversity.
Roland B. Dixon: Some aspects of North American archeology, in: American Anthropologist 15 (1913), pp. 549-577, hier S. 569.

1916
the cultural causes which account for the cultural diversity of peoples and ages persumably account for the prodigious cultural differences between individuals, the same causes being necessarily operative in the two instances.
Gustav Spiller: The interpretation of sociological data, in: American Journal of Sociology 21 (1916), S. 521-532, hier S. 529.

2) Kulturelle Vielfalt.

1930
this persistence of cultural diversity proved so disastrous to the Roman Empire at certain times
C. E. van Sickle: Particularism in the Roman Empire during the military anarchy, in: The American Journal of Philology 51 (1930), S. 343-357, hier S. 346.

1931
bis jetzt hat niemand im Lager der Einheitsstaatler den Weg gezeigt, auf dem die kulturelle Vielfalt des deutschen Volkes erhalten bleiben könnte, ohne seine staatliche Untergliederung zu bewahren.
Edgar J. Jung: Föderalismus aus Weltanschauung, München 1931, S. 69.

2004
Kulturelle Vielfalt […]
Aus der Sicht der rechtlichen Vielfalt bedeutsam ist, dass „Kultur“ offensichtlich von Anfang an ein Vielfaltsbegriff war, in dem ganz unterschiedliche und durchaus nicht nur „geistige“ Bereiche zu pfleglicher Behandlung zusammen-geordnet wurden; ein einheitlicher oder gar einförmiger Begriffsinhalt ist diesem Wort fremd, stets sprach es Heterogenes, nicht nur eine Mehrheit von Gleichartigem an. […]
In Vielfalt, nicht nur in Vielzahl, erscheinen Menschen, in der Vielfalt allein kann ihre Würde liegen ‒ zu allererst in ihrer wenn nicht nützlichsten, so doch schönsten Ausprägung der kulturellen Diversität: Menschenwürde entfaltet sich zu allererst im kulturstaatlichen Vielfaltsgebot. […] Kultur ist Vielfalt, geschaffen im Namen, in Ausnutzung von Freiheit(en). […]
Forschung […] kann nur aus und in Vielfalt wachsen, lediglich eine gleichgerichtete Vielzahl von Anstrengungen in ihr darf konvergierend orientiert [sein], Methodenvielfalt muss stets in Freiheit erhalten und gefördert werden. Forschung ist ein Vielfaltsbegriff. […] Kunst ist wohl noch viel weiterreichend vielfältig, aus Vielfalt erwächst sie und in ihr allein, zu immer neuer Vielfalt setzt sie sich fort. […] Kunstfreiheit ist also ein Vielfaltsbegriff par exellence. Mit der Verarmung der Kunstvielfalt beginnt der Untergang der Kultur, der Kulturstaatlichkeit. Kunstfreiheit ist rechtliches Vielfaltsgebot.
Anna Leisner-Egensperger: Vielfalt. Ein Begriff des öffentlichen Rechts, Berlin 2004, S. 70; 71; 73; 74.

2011
The new indifference to difference presents itself in theory as an approval of “cultural pluralism”: the political practice formed and is defined by the term supported by this theory ‘multiculturalism’. It is apparently inspired by the postulate of liberal tolerance and of support for communities’ rights to independence and to public acceptance of their chosen (or inherited) identities. In reality, however, it acts as a socialy conservative force. Its achievement is the transformation of social inequality, a phenomenon highly unlikely to win general approval, into the guise of ‘cultural diversity’, that is to say, a phenomenon deserving of universal respect and careful cultivation. Through this linguistic measure, the moral ugliness of poverty magically turns, as if by the touch of a fairy’s wand, into the aesthetic appeal of cultural diversity. The fact that any struggle for recognition is doomed to failure so long as it is not supported by the practice of redistribution gets lost from view along the way.
Zygmunt Bauman: Culture in a Liquid Modern World, Cambridge 2011, S. 46.

2018
the ‘default conception’ [is:] Culture facilitates the growth and stability of institutions; and if institutions are thought to have any affect on culture, it is to neutralize its political effects. Finally, cultural diversity is imagined principally as an absence: a lack of unity, coherence, and integration. Moreover, diversity has only one effect: it undermines social order, impeding communication, eroding common institutional rationality, and preventing value convergence. […]
The institution of multiculturalism brings to the fore a key issue: how particular kinds of social institutions can seek to construct authorized forms of diversity out of extant cultural heterogeneity. There is no such thing as culture that is unconditioned by social institutions, but institutions are often constructed with the explicit intent of reordering the cultural universe. Assimilation and genocide are designed to extinguish diversity, but other kinds of institutions – such as multiculturalism – celebrate diversity. In doing so, however, they authorize certain forms of identification and expressions of difference. Berrey draws a useful distinction between diversity as heterogeneity, and diversity as an organizational ideal. […] she shows that after the 1960s civil rights movement, corporations, universities, and government agencies institutionalized diversity policies. But instead of overcoming racial hierarchies, they simply reconfigured the racial order. […]
international orders develop particular kinds of institutions, which I term ‘diversity regimes’. Often the product of conscious design, but also evolving through piecemeal innovations, these are systems of rules, norms, and practices that simultaneously configure authority and organize diversity. Codified in legal instruments, embodied in formal institutions, and expressed and reproduced through informal understandings and social practices, these regimes do three things. First, they legitimize certain units of political authority, and define how they stand in relation to one another. These might be sovereign states, standing in relations of formal equality (as in today’s modern order). […] Second, diversity regimes authorize certain categories of cultural difference, and within these categories, they order difference hierarchically. In the early modern European order, for example, religion was the recognized axis of difference […]. Third, diversity regimes connect legitimate units of political authority with authorized categories of cultural difference. […]
Instead of seeing culture as a coherent deep structure, I see it as a realm of great variety, complexity, and contradiction. This heterogeneous cultural universe has structural effects, though. Order builders encounter it as a social reality, a reality that can generate all manner of identifications, mobilizations of meaning, and repertoires of practice, amenable to all kinds of political enlistment. Culture thus appears as a particular kind of governance challenge, affecting international order through the diversity regimes that order builders create in response.
Christian Reus-Smit: On Cultural Diversity. International Theory in a World of Difference, Cambridge 2018, S. 37; 207; 211; 221.