Do you remember the Korean guy/girl by the name of A who was really fluent in Japanese?
A was Korean but really good at speaking Japanese. Do you remember him/her?
この場合、次のような言い方ができますよ。
ーDo you remember the Korean guy/girl by the name of A who was really fluent in Japanese?
「韓国人の男性/女性で日本語がペラペラのAっていう名前の人覚えてる？」
A who was really fluent in Japanese で「日本語がとても流暢だったA」と言えます。
ーA was Korean but really good at speaking Japanese. Do you remember him/her?
「A さんは韓国人だったけど、日本語がペラペラだった。彼/彼女を覚えてる？」
good at speaking Japanese で「日本語を話すのが上手な」
ご参考まで！
カナダ 
