YOU SAID:

If a king does not speak the language of his kingdom, no one would understand him and he wouldn't be able to lead properly.

INTO JAPANESE

王が彼の王国の言葉を話さなければ、誰も彼を理解することができず、彼は正しく導くことができません。

BACK INTO ENGLISH

If the king does not speak the words of his kingdom, no one can understand him, he can not guide it properly.