While using "Spanish" I have changed the date format from mm/dd/yyyy to dd/mm/yyyy in Settings -> Languages.

I have:

-ensured that the users have Spanish as preferred language

-ensured that I logout and login again

-pressed CONTROL+F5 and even logging in a different browser to ensure that there was no previous cache messing up.

Dates still appear as mm/dd/yyyy.

I suspect that the first installation that I did in this server I chosed "US" as default language. Any idea?