In the English sentence, "on sale" could be taken to mean "for sale". Wiktionary says that in British English, this is a possible meaning for "on sale": https://en.wiktionary.org/wiki/on_sale
(e.g. "we've spent two years developing this product, and it's finally on sale").
(But I haven't yet checked whether e.g. "te koop" is accepted as a translation for "on sale" here)