All three cultures within the game have fairly diverse populations, though each culture tends to have a few dominant races in positions of authority. As for religion... All the cultures are very tolerant of religious diversity. In fact, it is actually viewed as "ODD" (or even in some cases a SIN) not to hold a belief in a greater authority. As honor and piety (a sense of right and wrong) are all closely related.
Just a few broad overview things about the world. The Zahkar society tends to be a more seafaring community whose cities and communities will be coastal. Their communities tend to favor a middle eastern type flair with minnerettes, plastered walls with murals and colorful silken canopies. The Hadhar society tends to be inland and have well-developed farmland resources. The Hadhar society tends to have a British/European feel with their communities being built more for function than form. The Elandary have very small communities that are highly nomadic. The Elandary are a very nature-oriented community.
Though very different, all the cultures have had significant interaction with one another, so you will see aspects of each of the cultures within each other. You will find that these cultures tend to have 4 guiding factors within their society: Honor, Family, Hospitality and Piety. The Zakharan and Hadharan societies tend to focus on Honor and Family. The Elandary culture tends to focus on Hospitality and Piety. No matter their differences, no matter the Gods that are worshiped... one common belief permeates these cultures... and that is the belief in "FATE". In fact, there are many Gods of "FATE" worshiped in the world.
Below is a brief description of what each society will tend to be like: