YOU SAID:

I speak for him who cannot speak for himself.

INTO JAPANESE

私は彼を彼自身のために話すことができない話します。

BACK INTO ENGLISH

I can't speak for himself in his talk.

INTO JAPANESE

彼の話で自分のため話せません。

BACK INTO ENGLISH

In his stories speak for themselves.

INTO JAPANESE

彼の話で彼ら自身のために話します。

BACK INTO ENGLISH

In his stories speak for themselves.