There are words that are used differently in North Korea and South Korea, but even within South Korean Korean, the sentence endings, vocabulary, and phrasing you should use can change a lot depending on the situation. The basic structure may be similar, but small differences matter.

Vocabulary changes depending on context, relationship, social distance, age, and whether the situation is public or private. North Korean speech is often more direct, but in South Korea, especially in more formal or higher-status social settings, speaking that directly can make a person sound crude or unsophisticated. Formal South Korean speech is often based on cushioning expressions. So even with the same Korean writing system, the rules for using sentences differ slightly.

This is something I feel even more strongly as a non-Western speaker participating on HN. If I do not use AI translation, many of my expressions become awkward. But after asking about it, I understand that even if the original Korean text was written without AI, using AI translation alone may cause the English version to be treated as Gen AI, which means I cannot really submit my blog posts.

So, reluctantly, I write my English comments by carefully combining machine translation, the English I have learned, and manual correction. Reading this article made me worry about how low-quality or awkward my comments may appear on HN.

And I'll bet that "Modern slang expressions — enthusiastically adopted by younger generations" is also difficult for elderly South Koreans; just as teenage British slang is foreign to this seventy year old Briton.

I suspect that a kind of class distinction and lack of shared recent history is behind most of the difficulty in socialisation rather then the language itself.

Móvil/Celular -cell phone-

Camarero/Mesero -waiter-

Tiroteo/Balacera -shooting-

Nevera/Heladera -freezer-

Cacahuete/Maní -peanut-

Coche/Carro -car- (In Iberian Spanish carro it's a old carriage)

Ordenador/Computadora (Computador was used in Ib. Spa. long ago maybe in 1960's and 1970's). And -computación (computing) it's used on formal, academical contexts, such as papers for the university.

Of course a formally written book will be understood everywhere, and the older, the better.