Well copyright is really complicated in global settings. But depending on how Korean copyright works, either the author owns the copyright, since copyright is created from the moment of publishing, or the publishers does. Well the one who owns it also has the exclusive rights to translations and more. They technically get copyright protected in every country that is a member of the Berne convention, which means that they from the first day of publishing get each country's specific copyright protection, so some countries might protect it less or more, but you have it.
So technically, this is not ok. But the copyright holder needs to do more than complain on twitter usually, they need to go through the infringers home country's legal hoops to rectify it.