YOU SAID:

I can't believe it ain't butter!

INTO JAPANESE

私はバターじゃないなんて信じられない!

BACK INTO ENGLISH

Can't believe I'm not butter!

INTO JAPANESE

バターではないなんて信じられない!

BACK INTO ENGLISH

Believe in butter!

INTO JAPANESE

バターを信じて!

BACK INTO ENGLISH

Believe in butter!