I have seen people claim that, when Oh Dae-su brawls with the group of teenagers, one of the reasons why they're making fun of him is that he speaks archaic Korean, a government-mandated update of the language having happened while he was confined. I've relayed that bit of trivia on to people several times, but I've since realized that I have no real proof of this, and I can't find that trivia anymore. Was there a language shift in real-world Korea for that time period? And is Oh Dae-su's dialogue in the more archaic form of Korean?
This may not be the proper forum for this discussion, but as no one has close-voted it...
I spent around 5 years working closely with older Korean business people and younger students, here in the Americas and also in Korea, and feel that I can make a few observations about the generational differences.
Around the turn of the last century, there was a trend in Korean education to adopt Western culture through language immersion. As there were many inconsistencies in values and attitudes between East and West, this caused some friction between older and younger generations (ironic because the older generations were actually fomenting this change).
This was reflected not just in lexis, but also in pronunciation. Here I am going to quote from an expert in Linguistics who is a Korean.
“…a new language ideology has been forming,…This shift occurs along with the changes in social climate and as Koreans are no longer viewed as citizens of what used to be “the hermit kingdom”, but see themselves as global citizens. As a result, phonemes which used to be seen as markers of immodesty are now finding their way into everyday spoken Korean.
…ideology is manifested through a widespread use of borrowed phonemes not found in Korean language in modern day Korean speech…
…may affect the (Korean) English speaker to feeling superior…”
In 1988, the Korean Board of Education issued a new mandate to standardize the language…loan words were divided into oykwuke and oylaye…students were asked to refrain from using foreign language...but young Koreans now do not place so much emphasis on distinguishing the difference.
Language Ideologies and Phonological Borrowing in South Korea -Hyojin Chi Kim
It is possible that that the generational difference was due to a government-mandated language shift, or possibly a phonemic shift occurring as part of the Westernizing of the language and culture.
[Edit] There is a government-mandated purification of the Korean Language going on in North Korea, but I didn't think it was relevant. The government is trying to eliminate words of Korean-Sino derivation.