Open your documents folder and browse to:
Open the file UTEngine.ini and search for Language=???.
MyGames>Unreal Tournament 3>UTGame>Config
Since your game is in Spanish the line will be:
Change it to the language you want (list of languages in the end of this post).
You might also want to change the default configuration file. To do that go to your steam folder and browse to the folder:
Once there open UTEngine.ini and do the same as for the other file (find Language=??? and replace with the default language you want).
steamapps>common>Unreal Tournament 3>UTGame>Config
Changing this last file will make so that if you delete your current configuration files in your documents, the new ones that'll be created will have the language you want.
List of Language:
CZE - Czech
DEU - German
ESN - Spanish
FRA - French
HUN - Hungarian
INT - International English
ITA - Italian
POL - Polish
RUS - Russian