I just did a fresh installation, and changed the locale to Spanish.
After doing that, I set the localization to the correct country (it's not Spain), and everything worked - except the digital clock format that remains at 24 hours and refuses to change to 12 hours plus AM/PM.
I configure the correct format in KDE Control Center, but the change does not make effect.
The same happens with any clock widget(digital or analog) placed in the desktop.
But the fuzzy clock is working correctly and it shows the time in 12 hours format, and in Spanish.
I tried removing the clock in the tray, and putting it again, but to no avail.