The most ancient and powerful race in the galaxy (or so they believe), the Protoss possess a highly structured society based on the preservation of their way of thinking. Highly intelligent and gifted with great psionic powers, they nevertheless suffer from a certain inflexibility that makes them extremely difficult to work with.
Originally the Protoss were divided into several warring tribes, but they were united by a single Protoss warrior/philosopher, Adun. He is apparently responsible for strengthening the psionic racial link that all Protoss share, and he developed the Khala, a strict religion, philosophy, and social structure. Under the Khala, the Protoss have mostly abandoned their tribal lines and divided into three castes: Khalai, artisans and inventors; Templar, warriors and explorers; and Judicator, administrators and leaders.
Terran dealings with the Protoss have been limited, restricting our knowledge of their abilities and equipment, but we do know that they possess extremely advanced technology, including warp-gate manipulation and energy shield generation. It is only recently that we have made significant progress in learning more about them.
Last month, a classified listening post along the Terran/Protoss border intercepted sensitive documents sent from a Protoss warfleet to their homeworld, Aiur. These documents are apparently part of a report on the current state of the Protoss military, and have been invaluable in expanding our knowledge of their capabilities.
Translating the Protoss language is never easy, as they prefer to rely on direct psionic communication wherever possible, but I believe that we have done an exemplary job. Latin has been used wherever we encountered one of the older, tribal tongues of the Protoss.