Gothic is split into two different versions, there is high gothic and low gothic.
High Gothic is the hieratic tongue of the Imperium, used in the titles of ancient institutions and organisations (such as the Adeptus Terra). It represents an older language than the commonly used Imperial Goverment Workers and is regarded as holy since it was the language used by the Emperor of Mankind. High Gothic is based of Church Latin used during the medieval age of ancient Europe.
High Gothic is also known as "Tech" because it is a version of the language in which the technical rituals of the Adeptus Mechanicus and other ancient works are recorded. High Gothic was first developed during the Dark Age of Technogly on Earth before the spread of mankind to its interstellar colonies. It derives from the common tongue of that time, an assimilation of English, European and Pacific languages which developed over many centuries in the North American, European and Pacific regions of Terra. High Gothic was the universal medium of written record until the Age of Strife, and was spoken as a first language by many and as a second language by almost everyone. Its idioms and vocabulary now appear archaic and mystic to the peoples of the present-day Imperium and many of its words have acquired religious significance over the years. It is the language of the tech-priests of the Adeptus Mechanicus and of forbidden books of heretical and daemonic lore.
High Gothic (represented in the game by pseudo-Latinized English) is unintelligible to most Imperial citizens. It is only the language of importants to Adeptus and members of the Inquitstion, and even among the perople who can speak it, it is only a second language. It is used only in formal situations, rather than as a casual language of conversation.
Low Gothic, a bastardized, present-day version of High Gothic, is the current common tongue of the Imperium. (Low gothic is basicly how we speak today, normal english)