YOU SAID:

His girlfriend would join them for dinner is what he said.

INTO JAPANESE

彼のガールフレンドは夕食のために彼らに参加するだろうと彼は言った。

BACK INTO ENGLISH

He said that his girlfriend would join them for dinner.

INTO JAPANESE

彼は彼女の恋人が彼らに夕食に参加すると言いました。

BACK INTO ENGLISH

He said her lover would attend them for dinner.

INTO JAPANESE

彼は恋人が夕食に出席すると言った。