Why does Orwell use words for which there are no English equivalents? Give some examples.

The use of Latin signifies not only a superior education and the class that goes with that (western values vs. values of the orient, which was how Burma was referred to), but also connotes religious values in that the traditional western Church, developing out of Rome, used (and sometimes still does use) Latin in its liturgy. In saecula secularum concludes various prayers, including the Lord's Prayer, and means in that context "forever and ever," and is geneally followed with a conclusive and affirmative "amen." (The literal translation, according to a Latin teacher I know, is "for centuries of all centuries"). Orwell uses the phrase and similar phrases ironically, to call attention to the very lack of holy motives behind England's imperialist agenda. One aspect of that agenda was to "convert the natives" to civilization and the religion that goes with that, which, as he shows in the story, might not be as righteous in its values as it pretends to be. Just as religion uses a form of terror (the fear of hell) to encourage people to "be good," so the colonialist regime imposes a reign of terror (in terrorem) to ensure people submit to the rules it imposes.