@Thifa You are indeed correct, and I'm ashamed to admit I didn't even pay attention to it when I read the chapter.
However, you are wrong about one thing: The Japanese lady wasn't actually an interpreter. She's an A class hunter who just happens to know Korean well enough to function as an interpreter. Though it might be difficult to remember with our Jinwoo being an SSS class hunter, but in reality an A class hunter is already a big mofo. There are only very few S class hunters, so they are a class of their own and globally recognised, but A class hunters are nationally extremely important people. So, she has no particular pride in temporally working as an interpreter. She has pride in being a hunter even if she lost the match here, but she wasn't afraid at all to have a match, which is the important thing. So, don't blame her for not behaving like a pro interpreter. The Japanese just didn't want to bring an ordinary person with them, so a real professional interpreter was out of the question.
It's pretty funny to think that if this was happening in Europe, everybody would just be talking in English with no need for an interpreter if the nations didn't have a common native language. However, in Asia it's taken for granted people can't communicate with each other unless they have special skills.