"We regret the translation error. The relevant services have been alerted and will make the correction immediately," the Spanish company said on its official Twitter account.
The gold chain with the offending caption was priced at 24.99 euros ($32).
An online petition organised by French actresses Aissa Maiga and Sonia Rolland and columnist Rokkaya Diallo, entitled "Slavery is not fashion", had on Monday attracted 1,604 signatures.
"This jewellery is meant to make an object of fantasy and fashion out of slavery," they said in the petition addressed to Mango's public relations department.
"Mango is trivialising tragedies... that still today have an impact on millions of human beings across the world," they added.
The caption in French read "collier (necklace) style esclave".
However, in Spanish "esclava", means a simple bangle or bracelet.