
Quinn K. answered 10/13/20
Advanced Korean Tutor with 2 years private tutoring experience
So, before the Korean war we had a relative uniformity in the North and South Korean "dialects", as it had all been united under the Choseon (조선) dynasty for hundreds and hundreds of years. However, after the 38th parallel (the line that originally separated North and South Korea) was implemented, we saw a shift in orthography for several reasons, with several outcomes:
-First, South Korea implemented numerous top-down pieces of legislature which created a legally-enforced standard for how Korean language would be written, pronounced, and read from that point on. Firstly, words that started with ㄴ- and ㄹ- saw these letters removed at the beginning of words: in a more famous case, "녀자"(girl) became "여자" (maintaining the same meaning), upon these grammatical mandates. However, North Korea did not see these same mandates, and thus the orthography stayed the same; in effect, "녀자" remains as the standard pronunciation in North Korea for "girl", and so would all other words that begin with ㄴ- or -ㄹ.
-We saw on both sides of the peninsula a feverous adoption of Hangul, but a much more universal and speedy adoption on the Northern side.
*For a bit of background, during the Choseon dynasty, the united Korean peninsula used "mixed Korean script" (국한문혼용), which mixed Hanja (Chinese characters with Korean pronunciation) for roughly 60% of the nouns/verbs, and native hangul characters for subject/object markers, grammatical particles and the remainder of nouns and verbs. A sentence "there is dragon a red dragon" in Mixed Korean would look something like "빨간龍이 있어요." In hangul, it would look like "빨간 용이 있어요." In that sentence, 龍 is the direct hanja translation for 용, and would be pronounced the same. In other sentences there might be more hanja, in others less.*
In essence, before the 38th parallel division, Mixed Korean script (Hanja+Hangul) was used for all literary writings in Korea, including records of soldier's diaries up until the Korean war. However, after the division, and especially after the Korean war, both sides drifted away from mixed script in a very big way, trying their best to reclaim hangul as the only accepted script within their respective countries. This was done mainly on nationalist principles, wherein anything non-Korean was not considered representative of the national identity. Nowadays, on both sides of the border, virtually all writings are in pure hangul, with only some political/religious texts remaining in mixed script on the southern side.
-Lastly, the way foreign loan-words developed was very different on either side, as most loan-words were adopted after the 38th-parallel division, when both sides were already culturally divided. In South Korea, we saw many words adopted form English words, and additionally some others from France, Germany, etc.: "konglish" is a famous phenomenon in South Korea, English words adopted directly into hangul script, such as "coffee/커피" and "haircut/헤어커트". In North Korea, loan words were adopted either directly from slavic languages, or where technological/mechanical concepts are translated directly into Korean using native Korean particles, so that "tractor" would be translated by combining the Korean particles "farm" and "machine" in order to create the new concept. This is part of the effort in North Korea to avoid as many foreign words in speech/writing as possible.
Finally, the respect markers at the end of words function a little differently in North and South Korea, and this has more to do with a cultural difference than a direct top-down decree. In the south, the respect particle "-습니다" is still used in high-respect situations, but unlike in South Korea, the middle respect particle -요 is much more rarely used, and thus 방말 (low respect, or common speech) is used in a lot of situations where in South Korea, the middle respect -요 particle would be used. Because of this, South Koreans interacting with North Koreans abroad often perceive North Koreans as a bit "rude" or "informal" for dropping the -요 particle in semi-formal situations.