YOU SAID:

We come here on a fool's errand.

INTO JAPANESE

我々 は無駄足にここに来る。

BACK INTO ENGLISH

We come here on the errand.

INTO JAPANESE

我々 は、用事でここに来た。

BACK INTO ENGLISH

We came here on business.

INTO JAPANESE

ビジネスでここに来ました。

BACK INTO ENGLISH

I'm here on business.

INTO JAPANESE

まあ　仕事でここにいるのよ

BACK INTO ENGLISH

Well, I'm here on business.

INTO JAPANESE

まあ　仕事でここにいるのよ

BACK INTO ENGLISH

Well, I'm here on business.