Shifting back and forth between languages probably wouldn't matter to people reading the English notes, though it might be annoying to people who can read Japanese or Korean. Should I maybe split the pool into two versions later, one for Japanese and one for Korean (with parent-child relationships for a few posts that might benefit from cross-referencing both versions like the skill name heavy ones)?

Usually I go with just one primary language for comics posted in two or more languages on Pixiv, but this one is tricky because the artist clearly intends the Japanese one to be primary starting the fourth arc and spends more effort typesetting it (so the overall art is better for the Japanese versions once typesetting is factored in), but the Korean version has slightly more information 'encoded' in the text.