[O] org-time-stamp, day format

[Uwe Brauer]

Hello

When I use org-time-stamp. I obtain:

 <2016-11-15 mar>

mar is short for martes, which is the Spanish word for Tuesday. How can
I can change that format, to any language I desire? I thought it would
be calendar-day-name-array but this seems not to be the case.

Thanks

Uwe Brauer