As one might expect from a story about animals, the language of Orwell's Animal Farm is fairly simple and unadorned, although it does have a certain formality characteristic of English prose from the mid-twentieth century (e.g., use of the word "shall"; almost complete avoidance of contractions).
A statistical analysis of the first four pages of the novel reveals rather brief sentences (10.2 words per sentence) and short words as well (4.2 characters per word). Orwell avoids passive verbs, using them less than seven percent of the time. Using the Flesh-Kincaid readability scale, we find that the first four pages of the novel score at a fourth grade reading level.
To be sure, we do find complexity of thought in the novel:
"A bird's wing, comrades," he said, "is an organ of propulsion and not of manipulation. It should therefore be regarded as a leg. The distinguishing mark of man is the HAND, the instrument with which he does all his mischief."
On the other hand, in an effort to impart the basic message of Animalism to all the animals, a certain degree of simplification is necessary:
After much thought Snowball declared that the Seven Commandments could in effect be reduced to a single maxim, namely: "Four legs good, two legs bad."
Thus, in Animal Farm, Orwell uses simple language to convey a rather complex allegory.