There are multiple hints of dictatorial times within the English language. For example, have you noticed how farm animals have Anglo-Saxon names (calf, cow, lamb, pig), whereas meat derived from the same animals has French-derived names (veal, beef, mutton, pork)? That dates back to the Norman conquest. The Anglo-Saxon farmers raised the animals, while the French-speaking Norman conquerors ate them.
A different example: are you familiar with the words 'khaki', 'chutney', 'mantra'? Those are all Indian in origin (source). Great Britain conquered a land, and then started borrowing ideas, and words for those ideas.
You want a fictional dictatorial power that speaks English. It's not enough to know that the power is a dictatorship. What values would it espouse? Would it look down at the "locals" and try to suppress their culture, like the Normans? In such a case, consider what words would be absent. Would it happily borrow words, like the British Empire? If so, consider what foreign words would see considerable use.
In 1984, George Orwell described a very particular dictatorship: one that deliberately suppressed thought. If you wish to suppress a people, you suppress their language (for example, in the USSR, Russian was taught throughout, while local languages were looked down on, not officially taught or used). If you wish to suppress an idea, you do not allow words that represent it. If you wish to suppress thought entirely, you deliberately limit vocabulary, which is what Newspeak was all about.
The Purpose of Newspeak was not only to provide a medium of expression for the world-view and mental habits proper to the devotees of Ingsoc, but to make all other modes of thought impossible. It was intended that when Newspeak had been adopted once and fir all and Oldspeak forgotten, a heretical thought - that is, a thought diverging from the principles of Ingsoc - should be literally unthinkable, at least so far as thought is dependent on words. [...] Newspeak was designed not to extend but to diminish the range of thought, and this purpose was indirectly assisted by cutting the choice of words down to a minimum. (George Orwell, 1984, Appendix - The Principles of Newspeak)
Resistance movements too influence language, and insert words. Consider 'samizdat', which managed not only to become a Russian word, but to find its way into English vocabulary.