1. No, "backsliding of history" is not correct. History cannot backslide; it is simply the record of what happened. Better would be "historical backsliding" (of those politicians who created the policy) The word "backsliding" mostly refers to moral failure, but it can refer to regression in general, so I don't see any objection to its use. Here are a few examples of contemporary usage. -Is East-Central Europe Backsliding? From Democracy Fatigue to Populist Backlash -Facebook's Valuation Is Suddenly Backsliding Ahead Of The IPO Filing 2. "Prohibiting importing" is awkard. Better would be "Prohibiting the import/importation" totally....I don't like the use of the adverb here modifying "sign". Better would to use it as an adjective modifying "backsliding". sign of total historical backsliding. Prohibiting the import of Western cultural products such as American movies is a sign of total historical backsliding.

I'm sorry I don't understand what you are trying to express here. The sentence does not make sense at all. Maybe you can give us the Chinese and we can help translate it for you.

"Backsliding, also known as falling away is a term used within Christianity to describe a process by which an individual who has converted to Christianity reverts to pre-conversion habits and/or lapses or falls into sin, when a person turns from God to pursue their own desire." ( taken from Wikipidea) It is not suitable for use in your sentence. And I have never heard it used in other context!

You have too many words that don't belong. 'Prohibiting the importation of Western culture, in the form of movies and music is a sign that nothing has really changed'

Sorry, there are a number of grammar mistakes in the sentence from the very beginning. By the time I read "such movies", the sentence is completely nonsensical. The use of "totally" is inappropriate (it actually sounds comical). Could you explain what you are trying to say (if the sentence is yours)? To answer your question, "backsliding of history" needs "the". Even then, it still doesn't make much sense in the sentence.