The Universal Translator is a small, handheld computer that can translate alien text messages to Earth English. In the Unreal single player game, it is discovered in the prison area of the Vortex Rikers by Prisoner 849.
The Universal Translator helps the player decipher notes, signs, and other items with alien text, usually in the languages of the Nali or the Skaarj. Every time the player comes in the vicinity of such an item, the device alerts the player of a new message with a sound. (These events are called "Translator Events" in the game's code.) The device is mapped to a shortcut key "F2", which shows the translated message in the device, or removes the message when pressed again.
Single player maps made by fans usually contain a Universal Translator at the start.
Trivia
Originally the Universal Translator would also read hint messages found throughout the game, but this feature didn't make it into the final game.