According to the recent update by the South Korean National Tax Service (NTS), any foreign who work or worked in Korea shall fill up their year-end 2018 tax settlement by the end February 2019, that regardless of their nationality or the length of stay.
The report can be done online and the Korean National Tax Service provide English guide for it. For more information please check their website: https://www.nts.go.kr/eng/index.asp
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