Welsh language tutor Jonathan Ford spotted the signs at the Bedwas Co-operative in Caerphilly county after its £360,000 refit. He said the mistake made him laugh but that some Welsh speakers would be "cross".
A Co-operative spokesman said: "We will remove these signs and replace them as soon as possible. We would like to thank the customer for pointing this out."
Supermarkets in Wales are not obliged by law to have bilingual signs.