An outrageous or scandalous act; something so unacceptable or absurd that it is beyond words.
そんな横領行為は言語道断だ。
Such embezzlement is outrageous.
彼の無責任な発言は言語道断で、会社は謝罪した。
His irresponsible remarks were inexcusable, and the company apologized.
子どもを暴力で叱るのは言語道断だ。
It is outrageous to punish a child with violence.