Korean is the national language. It’s worth noting that North Koreans prefer to call Koreans Choseonmal rather than hangungmal. North Korea, unlike South Korea, has abandoned Chinese hanja characters in favor of Choseongul, or hangeul characters.
Your guides will speak English reasonably well (some better than others) and will translate if necessary. Mandarin, German, Russian, Japanese, or Spanish are among the languages spoken by some guides.
Although there is no official rule prohibiting residents of the DPRK from engaging with visitors, locals may be discouraged from communicating with foreigners owing to government propaganda that suggests outsiders are usually up to no good, and language may be an additional obstacle. A trip to the DPRK during their holidays may allow you to engage more with the people.