North Korea is extraordinarily homogenous as every person (other than a small group of Chinese in the north) is ethnically Korean. The Koreans are probably most closely related to the people of Manchuria (in modern day China), making them more distantly related to the Altaic people of Mongolia and the Turkic people. There are also some ethnic similarities to the Japanese, but again this is a distant relationship.
Korean is the only official language of North Korea. This language is unique in that it has no close relatives; some people believe it is distantly related to the Altaic Languages, but this is debated. The Altaic languages include Mongolian, the Turkic languages, and arguably Japanese.
North Korea doesn't teach foreign languages other than a few key phrases in English to their military, such as "hands up" and "put down your guns and surrender." However, most governmental tour guides do speak English, which is the language most tours are given in.
Religion is all but outlawed in North Korea. There are some government-sponsored religious groups that exist, perhaps to provide the illusion of religious freedom or perhaps as a medium to spread government propaganda. Some visitors to the country argue that there is an almost religious reverence by the people to the government and their leaders. Traditionally, and perhaps still in practice to a very small degree, the people tend to be Buddhist, Confucianists, and Christian.