I'm Japanese, and I can still usually spot AI-generated Japanese by its word choice. Some words, like 実務 (practical work) and 帳簿 (a ledger), turn up far more often than they should. Casual ones like 効く (to work well, to be effective) and 刺さる (to pierce > to resonate, to hit home) get used where another word would normally be the first choice. They're the Japanese equivalent of "delve." I'm not a native English speaker, but my impression is that AI-generated English has improved a lot recently ...