Hi,
If you force your site to use Spanish culture it should also make the RPX widget use Spanish.
It should be as simple as adding this to your user.config
<add key="UseCultureOverride" value="true" />
<add key="site1culture" value="es-ES" />
then touch your Web.config to make it reload settings.
As documented at the bottom of this page:
http://www.mojoportal.com/localization.aspx
Hope it helps,
Joe