What is the language technique in this Animal farm quote: "That evening Squealer explained privately to the other animals that Napoleon had never...

This is an example of double-talk, or propaganda. Napoleon, who had been opposed to the windwill, now asserts through a clever lie that the windmill had been his idea all along, an inversion of history that is politically expedient. In fact, what the quote shows and that, history, and even truth itself, can be made into any shape the ruling class, in this case Napoleon, wants it to be.  As  puts it:

What...

This is an example of double-talk, or propaganda. Napoleon, who had been opposed to the windwill, now asserts through a clever lie that the windmill had been his idea all along, an inversion of history that is politically expedient. In fact, what the quote shows and that, history, and even truth itself, can be made into any shape the ruling class, in this case Napoleon, wants it to be.  As  puts it:

What is most demoniacally human about the pigs is their use of language not only to manipulate the immediate behavior of the animals through propaganda, emotive language, and meaningless doubletalk but also to manipulate history, and thus challenge the nature of actuality.

The  concepts of "truth" and "falsehood" become empty signifiers in this kind of speech, in that the final determiner of what is "true" or "false" is not reality or experience but the state.