Both the Enhanced and Classic Client have the option of playing in a number of languages. For the Enhanced client there is a selection menu in the options.
For the Classic Client it is a bit more difficult. You need to go into your Ultima Online folder and edit uo.cfg and change the option within the UserLanguageCodeString=ENU, the options are:
DEU (German)
ESP (Spanish)
FRA (French)
CHT (Chinese)
CHS (Non-Traditional Chinese)
JPN (Japanese)
KOR (Korean)
So for you, you want it to read UserLanguageCodeString=ESP.
This should still work, the support I don't believe was removed. If it doesn't work, you may have to change it for each individual character as well with the same procedure.