"저는 한국에 없습니다."
Translation:I am not in Korea.
Not because you're studying Korean. That also doesn't make you a koreaboo. But because of the hundreds of "ARMYYYYYY" and other irrelevant, nonsense messages that are flooding these discussion boards, making it impossible to find useful information and learn anything. This happens for no other language, only Korean. It doesn't have to be all serious, some relevant humor is fine, but this is just annoying asf.
It's the online equivalent of loud, annoying kids disrupting class continuously, ruining it for everyone else.
Koreans don't call their country "South Korea", and 한국 is only an abbreviation of the full name 대한민국. Even in English that's not an official name, it's the "Republic of Korea".
For political reasons the Korean government would never officially call itself "South Korea", this would make the division seem permanent, and legitimize the other side.
-ga is a topic marker. -neun is subject marker. here the subject is I. you might want to check this out https://medium.com/story-of-eggbun-education/basic-topic-marker-%EC%9D%80-eun-%EB%8A%94-neun-vs-subject-marker-%EC%9D%B4-i-%EA%B0%80-ga-48d20f1008d9
없다 means "to not exist", "to lack", or also "to not have". It's the opposite of 있다 (to exist or to have). In 한국에, 에 means "in" or "at".
If we translate it literally, "저는 한국에 없습니다." is "I don't exist in Korea.", but that definitely means "I'm not in Korea."
Just like how the opposite "저는 한국에 있습니다." (literally "I exist in Korea") means "I'm in Korea."