language files don't work

I recently updated WP e-commerce to V 3.8.9 and found out that the language files don’t work. I changed some texts in wpsc-es_ES.po but they don’t show up onlne.

I found out that other people have same trouble into translating “Price” for example. It does not work.

https://www.ads-software.com/extend/plugins/wp-e-commerce/