Produced by: Azarael (Portuguese) and Iolo (Spanish)
Website: Traducción Ultima (Spanish)
There are two known fan-made translation patches for Ultima Underworld.
The Portuguese translation is not quite complete. A full translation does (or did) exist, but it is no longer available for download from the developer.
The Spanish translation, on the other hand, is complete, and is one of a series of Spanish Ultima translations that have appeared within the last couple of years.