There are three 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 Russian translation, equally, is also not entirely complete. The game’s text (e.g. dialogue) has been translated, but graphical elements bearing English text have not yet been modified.
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.