has been stemmed for causing labor shortages in various skilled blue collar labor and vocational occupations, where many go unfilled as the negative social stigma associated with vocational careers and not having a university degree continues to remain deep-rooted in South Korean society. Language Korean is the official language of South Korea, and is classified by most linguists as a language isolate. It incorporates a significant number of loan words from Chinese. Korean uses an indigenous writing system called Hangul, created in 1446 by King Sejong, to provide a convenient alternative to the Classical Chinese Hanja characters that were difficult to learn and did not fit the Korean language well. South Korea still uses some Chinese Hanja characters in limited areas, such as print media and legal documentation. The Korean language in South Korea has a standard dialect known as the Seoul dialect (after the capital city), with an additional four dialects (Chungcheong, Gangwon, Gyeongsang, and Jeolla) and one language (Jeju) in use around the country. Almost all South Korean students today learn English throughout their education, with some optionally choosing Japanese or Mandarin as well. Religion According to the results of the census of 2015, more than half of the South Korean population (56.1%) declared themselves not affiliated with any religious organizations. In a 2012 survey, 52% declared themselves "religious", 31% said they were "not religious" and 15% identified themselves as "convinced atheists". Of the people who are affiliated with a religious organization, most are Christians and Buddhists. According to the 2015 census, 27.6% of the population were Christians (19.7% identified themselves as Protestants, 7.9% as Roman Catholics) and 15.5% were Buddhists. Other religions include Islam (130,000 Muslims, mostly migrant workers from Pakistan and Bangladesh but including some 35,000 Korean Muslims), the homegrown sect of Won Buddhism, and a variety of indigenous religions, including Cheondoism (a Confucianizing religion), Jeungsanism, Daejongism, Daesun Jinrihoe, and others. Freedom of religion is guaranteed by the constitution, and there is no state religion. Overall, between the 2005 and 2015 censuses, there has been a slight decline of Christianity (down from 29% to 27.6%), a sharp decline of Buddhism (down from 22.8% to 15.5%), and a rise of the unaffiliated population (from 47.2% to 56.9%). Christianity is South Korea's largest organized religion, accounting for more than half of all South Korean adherents of religious organizations. There are approximately 13.5 million Christians in South Korea today;