YOU SAID:
I ate potatoes yesterday
INTO JAPANESE
昨日ジャガイモを食べた
BACK INTO ENGLISH
Yesterday I ate the potatoes
INTO JAPANESE
昨日、ジャガイモを食べた
BACK INTO ENGLISH
Yesterday, I ate the potatoes
INTO JAPANESE
昨日、ジャガイモを食べた
BACK INTO ENGLISH
Yesterday, I ate the potatoes
That didn't even make that much sense in English.