What sort of changes did you have in mind? Government-based attempts to shift the direction of language have been frequent throughout history, either through changes in language policy and planning efforts, often for the sake of modernising the language as much as limiting dissent, but also in the form of attempting the limit certain things somewhat like what you propose. However:

As I learn more about different languages it becomes clear how much power there is in simply not having the words to express dissent.

That's not really how language works. Controlling the words which are permissible for public use is not the same as ridding the language of the words. Throughout history when governments have attempted to limit specific words either through active censorship by the state or by imposing self-censorship, people have managed to work around the limitations.

As an example, in Republican China there was significant censorship of both the press and the arts. Criticism of the government, pointing out corruption and other things that might not show the government in a good light was restricted. This did not prevent people from criticising the state. They weren't without the language to make the criticisms. It's just that they were unable to be published.

The notion of newspeak as described in Orwell's 1984 hasn't really happened in any significant way in human history. Like I said above that's not how language really works. Even in the most restrictive periods of China's history (sticking to China since that's what I know better), it's never been as pervasive as outlined in fiction. At no point was the environment repressive enough for long enough that it made a significant enough shift in that direction, and even if it were, those who would dissent would not be prevented from doing so simply because the state convinced them to stop using certain words.

There's a discredited theory called "linguistic determinism". It's the idea that you see thrown around Reddit like how if your language lacks the word for blue it means you can't perceive the colour blue. I say discredited because there's not really anything to it. Lacking a word for blue doesn't mean you can't see blue. It just means that when you see blue, you might classify it as a shade on one end of green, but you're still seeing the colour that someone else might classify as blue.

Likewise, lacking a word to express how you dislike your government doesn't actually mean you can't dislike your government, and if there's a significant value in having a word for the concept, one will inevitably be coined or borrowed for that purpose.

His Newspeak was what the Formalists believe all language was like. They believed that "speech control" is done all the time and in all the countries and the task of a writer being teaching the people to think for themselves by playing with the preconceived notions.

You shouldn't forget that Orwell was a Marxist as well, and that his criticism of Stalin Russia was drawn from Trotsky complaining about the Bureaucratisation and of the USSR not being any different from the "Bourgeois" countries.

In Russia formalism fell out of grace in the 1930s and in 1948 all the formalists would get purged.

In 1950 Stalin himself wrote an article that criticised linguistic determinism in the Pravda.

Orwell might have been giving them tribute.

Here you can read what aesthetic theories replaced formalism later in China and USSR.