Surprisingly, no answer has yet produced the most obvious examples of what Eco meant in the essay, which the author himself gave directly following the quote given in the question: the language used by the original fascists, Mussolini's National Fascist Party.
On the morning of July 27, 1943, I was told that, according to radio
reports, fascism had collapsed and Mussolini was under arrest. When my
mother sent me out to buy the newspaper, I saw that the papers at the
nearest newsstand had different titles. Moreover, after seeing the
headlines, I realized that each newspaper said different things. I
bought one of them, blindly, and read a message on the first page
signed by five or six political parties — among them the Democrazia
Cristiana, the Communist Party, the Socialist Party, the Partito
d’Azione, and the Liberal Party. Until then, I had believed that there
was a single party in every country and that in Italy it was the
Partito Nazionale Fascista. Now I was discovering that in my country
several parties could exist at the same time. Since I was a clever
boy, I immediately realized that so many parties could not have been
born overnight, and they must have existed for some time as
The message on the front celebrated the end of the dictatorship and
the return of freedom: freedom of speech, of press, of political
association. These words, “freedom,” “dictatorship,” “liberty,” — I
now read them for the first time in my life. I was reborn as a free
Western man by virtue of these new words.
This perfectly represents the "impoverished vocabulary" mentioned in the quote given in the question, and clarifies Eco's meaning quite well. Unlike what the question asserts, Eco did not believe that the restriction of language was only possible in fiction. The fascist government of Mussolini apparently pushed words like "freedom" and "dictatorship" so far to the margins of society that an moderately educated 11-year-old could have no concept of them. Eco implies that this helped build the idea that having a single party that governed society was both natural and inevitable. This is perfectly in line with the Newspeak of 1984, in which eliminating words from the language, particularly when not replaced with other vocabulary, is a standard tool.
Most of the other answers talk about language that is (or that the question writers believe to be) euphemistic, or to framings of issues that exclude diverse or heterodox perspectives. While potentially conceptually related to the ideas that Eco is talking about, this is unlikely to be Newspeak in the sense that he means, which appears to be the main way in which Orwell used it in his book, the simplification of vocabulary and language structure in order to reduce the possibilities of dissent. Newspeak does not primarily seek to stigmatize the use of negative terminology to refer to Big Brother or the expression of ideas contrary to him, which is cause enough for execution and torture in any sense: it tries to restructure the language in such a way that it becomes impossible to say, not only that Big Brother is a dictatorship and the people of Airstrip One are not free, but even that any country, even whichever one is supposedly Oceania's enemy, is unfree.
There is certainly some element of euphemism in phrases like joycamp (labor camps) or Minipax (the Ministry of Peace, in charge of waging perpetual war) but that euphemism is not enough concepts themselves must be eliminated. That is the essence of Newspeak.
As such, contrary to the question, linguistic reform and control has often been important to fascist governments. In 1944, for instance, Hitler planned a spelling reform that would have simplified the complexity of the language by changing words of non-German origin to be written in accordance with German pronunciation: not particularly malevolent in itself, perhaps, but well in line both with the "impoverishment of language" principle of ur-fascist Newspeak mentioned by Eco, and the need of a nationalist regime to exalt what it views as distinctive about its country at the expense of any foreign influences.
Although, as mentioned previously, euphemism was not a central part of Newspeak in 1984, it still played a role. As Eco noted, euphemism for euphemism's sake is not particular to Newspeak: the purpose of euphemism in Newspeak is primarily to displace words from the language altogether. If one can condemn the enemies in specific terms, one can also condemn the regime, something that a totalitarian government cannot tolerate. Consider, for instance, the usage of the term Sonderbehandlung in Nazi Germany. It was used not only to refer to the systematic killing of Jews and other "undesirables," but also to execution of Germans opposed to the regime, and even, seemingly, in contexts entirely unrelated to execution. This is the impoverishment of language that Eco refers, and is classic Newspeak: "execution" as a concept ceases to exist. Anything up to and including the worst atrocities can be incorporated into the concept of Sonderbehandlung.
These tendencies are reflected in many modern authoritarian and totalitarian movements of various political orientations, though often ones that would be considered considerably milder than Nazism or Italian fascism.
For instance, a recent bill introduced by the Republican Party of the USA would stipulate the following:
Notwithstanding any other provision of law munder this act to the
contrary, beginning with the 2021-2022 school year, the board of a
school district or the board of directors of a public school academy
shall ensure that the curriculum provided to all pupils enrolled in
the school district or public school academy
does not include coverage of the critical race theory, the 1619
project, or any of the following anti-American and racist theories...
This bill not only seeks to specify a particular curriculum through standards that are quite questionable on their own merits and seem largely motivated by the desire to avoid discussion of anti-racist concepts that make the Republican Party uncomfortable, but also, and more relevantly for the purpose of this answer, would prohibit any coverage of "critical race theory," which presumably encompasses positive, negative, or deconstructive coverage, and would effectively amount to a prohibition on any discussion of the term in the affected school systems, thus eliminating it from a particular educational ambit: a central element of Newspeak, as Eco defines it.
In a similar but more extreme vein, the CCP in China also seeks to eliminate words and phrases that it views as a threat to the government. For instance, talking about "lifelong control" was prohibited on Weibo in the wake of Xi Jinping gaining precisely that, and allegedly even the word "disagree" was considered at least temporarily off-limits.
These modern successors to Eco's Newspeak continue to illustrate the basic idea: to eliminate words that are considered a threat to the governing power. Mere euphemism or dysphemism, the replacement of a word by another that denotes a similar concept, does not appear to be a major part of Eco's Newspeak, nor does stigmatization of the use of certain concepts in combination, though both of these can be tools of control: the key is to restrict and confine the language so that it becomes difficult, not simply to express ideas in a way that offends the status quo, but to express them at all.