how did corruption or malnupulation of political language enable the pigs in animal farm to turn democracy into tyranny.

This question compromises much of the book. The pigs, Napoleon in particular, take their cue from the human world and exploit the farm animals even further. Manipulation through fear and fascist ideology turn the farm from an initial utopia to a dystopia. Check out the summary in the GradeSaver link below,

http://www.gradesaver.com/animal-farm/study-guide/short-summary/