I never learned Japanese in school cause we took English classes instead, so I would say google translate for a majority of them. I can only think of a few Korean players, like Astell, who seem to be fluent in Japanese. So probably just google translate
not sure how you would say all of them are good in Japanese, the only Korean players that I know that are good and fluent in speaking Japanese is Astell and probably Medusa. so most likely its the translation machine like deepL or Papago that they use.
I did know Medusa is good in Japanese, and yeah Joxjo is good at them as well, but Astell is probably the most fluent one in terms of the speaking proficiency but still that doesn't imply that all of the KR players are actually good in Japanese.
english is taught in korean schools, not japanese. but compared to english, japanese is much more easier for koreans to learn because of the similarities in grammar and sentence structure (same as japanese finds it easier to learn korean).
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