Korean regional stereotypes
Gyeongsang: Fiery, hot-tempered and impatient. A lot of this is reinforced by the regional dialect, which shortens a lot of words. It also actually has tones, unlike other regional dialects in Korean. They're perceived to be loud and to stand their ground, although they also have reputations of loyalty to their friends. Politically conservative.
Jeolla: Unfortunately the most discriminated region, often disliked by other regions. Left-wing (not untrue, there is a huge voting bias toward progressive candidates and parties). As they are discriminated by others, there is the perception that they only look out for other fellow Jeolla people. Gyeongsang people would say that Jeolla people are not trustworthy. Due to their regional discrimination they are also most likely to 'hide' their regional dialect and background.
Chungcheong: Slow, chilled, unpretentious. This is also 'shown' in the regional dialect, which tends to elongate the ends of words. Often the swing province in elections, not as politically nuanced as the above.
Gangwon: Rural, country bumpkins. POTATOES! CORN! Arguably the Gangwon area is one of the least urbanised. The image that people have of the area is farmland. Also lots of snow- so it's also a major winter holiday destination. Tend to vote more conservatively.
Gyeonggi (Seoul metropolis): Urban. Uppity Seoulites. Wussy city people who can't deal with the countryside. Tend to vote more progressively.
Korean dialects
Seoul/Gyeonggi: It may be a bit odd to call Seoul accent a "dialect," at least in a sense that the word is used to describe that deviates from the standard language. This is so because the National Institute of Korean Language decreed that the standard Korean shall be: "modern Seoul language used generally by educated people." In other words, Seoul accent is the standard Korean, and all Koreans are educated to speak like a Seoul person. Thanks to universal public education and mass media, most Koreans actually do. Even Koreans who grew up with an accent can usually shift in and out of the "standard Korean" depending on the circumstance.
This is not to say that the Seoul/Gyeonggi dialect is exactly coterminous with standard Korean. Compared to standard Korean, Seoul/Gyeonggi dialect consistently mispronounces certain words in a certain pattern. For example, this dialect often replaces ㅗ ("oh") with ㅜ ("ooh"), such that 삼촌 ("uncle", pronounced "samchon") would be pronounced like 삼춘 ("samchoon"). There are other differences between Seoul/Gyeonggi dialect and the standard Korean language, but they are so subtle that discussing them would only confuse most people. Let's move on to the more obvious accents.
Chungcheong: Being that Chungcheong-do is somewhat close to Seoul, Chungcheong accent is still pretty close to the standard Korean. One difference, however, is immediately noticeable in a major Chungcheong-do city like Daejeon--everyone speaks slowly. The long-standing joke about Chungcheong accent goes like this: a father and a son was walking up the hill, when the son saw a huge boulder rolling down the path. The son said: "Faaatheer, therrre iiiiiiss a bouuuuulderrr rollllllling dowwwwwwn." Before the son could finish the sentence, however, the boulder had already rolled down and killed the father.
Chungcheong dialect also more commonly replaces ㅗ with ㅜ, and ㅛ ("yo") with ㅠ ("yu"), especially with verb conjugations. So instead of "하세요" ("haseyo", "please do"), a Chungcheong dialect would say "하세유" ("haseyu"), or shorten it to "하슈" ("hasyu").
(Side note: because the Korean Father is from Chungcheong-do, the Korean himself sometimes reverts to this dialect.)
Gangwon: Although Gangwon is a large province in terms of area, the high Taebaek mountain range that bisects the province meant that historically, relatively few people lived in the Gangwon area. Because there were less people living in the area, Gangwon did not really develop a highly distinctive dialect. This is particularly true as to the western part of Gangwon (e.g. with cities like Hongcheon, Chuncheon, etc.) which has no physical barrier between it and Seoul.
But the part of Gangwon that touches on the eastern coast of Korea (also known as "Yeongdong" region, i.e. "east of the mountains") did develop a fairly unique dialect, as the steep mountains cut off much of the exchange with other regions. Unlike standard Korean (=Seoul dialect,) Gangwon dialect uses tones to distinguish the meaning of homo-phonic words, like Chinese or Vietnamese do. It also has a number of words that are very unusual to speakers of standard Korean, such as 콩칠팔새삼육하다 ("to banter") or 맨자지 ("white rice").
This is not to say that the Seoul/Gyeonggi dialect is exactly coterminous with standard Korean. Compared to standard Korean, Seoul/Gyeonggi dialect consistently mispronounces certain words in a certain pattern. For example, this dialect often replaces ㅗ ("oh") with ㅜ ("ooh"), such that 삼촌 ("uncle", pronounced "samchon") would be pronounced like 삼춘 ("samchoon"). There are other differences between Seoul/Gyeonggi dialect and the standard Korean language, but they are so subtle that discussing them would only confuse most people. Let's move on to the more obvious accents.
Chungcheong: Being that Chungcheong-do is somewhat close to Seoul, Chungcheong accent is still pretty close to the standard Korean. One difference, however, is immediately noticeable in a major Chungcheong-do city like Daejeon--everyone speaks slowly. The long-standing joke about Chungcheong accent goes like this: a father and a son was walking up the hill, when the son saw a huge boulder rolling down the path. The son said: "Faaatheer, therrre iiiiiiss a bouuuuulderrr rollllllling dowwwwwwn." Before the son could finish the sentence, however, the boulder had already rolled down and killed the father.
Chungcheong dialect also more commonly replaces ㅗ with ㅜ, and ㅛ ("yo") with ㅠ ("yu"), especially with verb conjugations. So instead of "하세요" ("haseyo", "please do"), a Chungcheong dialect would say "하세유" ("haseyu"), or shorten it to "하슈" ("hasyu").
(Side note: because the Korean Father is from Chungcheong-do, the Korean himself sometimes reverts to this dialect.)
Gangwon: Although Gangwon is a large province in terms of area, the high Taebaek mountain range that bisects the province meant that historically, relatively few people lived in the Gangwon area. Because there were less people living in the area, Gangwon did not really develop a highly distinctive dialect. This is particularly true as to the western part of Gangwon (e.g. with cities like Hongcheon, Chuncheon, etc.) which has no physical barrier between it and Seoul.
But the part of Gangwon that touches on the eastern coast of Korea (also known as "Yeongdong" region, i.e. "east of the mountains") did develop a fairly unique dialect, as the steep mountains cut off much of the exchange with other regions. Unlike standard Korean (=Seoul dialect,) Gangwon dialect uses tones to distinguish the meaning of homo-phonic words, like Chinese or Vietnamese do. It also has a number of words that are very unusual to speakers of standard Korean, such as 콩칠팔새삼육하다 ("to banter") or 맨자지 ("white rice").
Gyeongsang: Also known as "Yeongnam" region, this large and populous region speaks with a strong, harsh accent, befitting its stereotype of being the land of manly men. Compared to the mild and flat Seoul accent, Gyeongsang dialect is dynamic with high peaks and low valleys in its speech. Like Yeongdong dialect, Gyeongsang dialect uses tones to distinguish the meaning of homo-phonic words.
One prominent feature of Gyeongsang dialect is the inability to pronounce certain sounds that appear commonly in Korean. For example, Gyeongsang dialect speakers are unable to pronounce ㅆ when it appears as the beginning sound of the word, leaving them unable to properly pronounce 쌀: "rice", one of the most commonly used words in Korea. (Instead, Gyeongsang-do dialect speakers are forced to say 살.) Gyeongsang-do dialect is also missing the vowel sound for ㅡ ("eu"), which is instead pronounced as ㅓ ("eo"). So if a Gyeongsang-do person is faced with the word 음악 ("music"), she is likely to pronounce it as 엄악.
Gyeongsang dialect also has trouble with compound vowels, such as ㅘ or ㅢ. In many cases, Gyeongsang dialect drops the first sound of the compound vowel. So 사과 ("apple") is pronounced like 사가, and 의사 ("doctor") is pronounced like 이사. Former President Kim Young-sam, who was not only from Gyeongsangnam-do but also was a George W. Bush-esque mangler of words, often faced snickers when he would give a speech about promoting 관광산업 ("tourism industry")--because his inability to pronounce the consecutive ㅘ, and his penchant for not enunciating words, made him sound like he wanted to promote 강간산업 ("rape industry").
Jeolla: Also known as "Honam" region, this southwestern region also developed a highly distinctive dialect of its own. Jeolla dialect is slower than Seoul's, but faster than Chungcheong's; it has more ups and downs in sound, but not as much as Gyeongsang dialect.
Jeolla-do dialect often adds extra ㅅ and ㅂ in within certain words. For example, 저어라 ("stir") is pronounced as 젓어라, and 더워 ("hot") is pronounced as 덥어. Often, ㅏ and ㅓ are pronounced as ㅐand ㅔ, such that 마음 ("mind") is pronounced as 매음 and 떡 ("rice cake") is pronounced as 떽.
The most distinctive part of Jeolla dialect is the vowel conjugations that end a sentence. The most commonly known characteristic is the tendency to finish sentences with an extraneous 잉. (Example: 재미없다 --> 재미없다잉, "[This is] not fun.") Vowel conjugation ~요, which creates a formal honorific, is ~이라 or ~어라. (Example: 좋구만요 --> 좋구만이라 ("[This is] nice."); 다 먹었어요 --> 다 먹었서라 ("[I] finished the food.")) Vowel conjugation ~데 is ~디 in Jeolla dialect, such that 그런데 is 그런디.
Jeju: The largest island of Korea is also the most geographically isolated population center. As such, proper Jeju dialect is nearly a separate language from Korean. In fact, in 2011, UNESCO listed Jeju dialect as "critically endangered language," which means UNESCO considered Jeju dialect to be a separate language.
Jeju dialect is grammatically Korean, but a lot of its vocabulary is nearly unrecognizable to mainland Koreans. This is so because Jeju has been so isolated, it has preserved extremely old Korean words. It also has imported words from Japan, China and Mongolia--the last from Mongolian invasion of Korea in the 14th century (!). Words like 송키 ["vegetable"], 오름 ["mountain"], 야개기 ["neck"], 가사 ["umbrella"] have tenuous connection to mainland Korean.
Vowel conjugation is also significantly different in Jeju dialect. Basic honorific is ~ㅂ서, which replaces ~요. (Example: 오세요 --> 옵서 ["Please come."]). Honorific question is ~꽈, instead of ~ㅂ니까 . (Example: 아닙니까? --> 아니꽈? ["Isn't it?"]).
