I'm not. The letter contains Chinese writing that is not translated in the post, however I'll wager it attempts to add clarity in Chinese to what the author assumes may be inadequate English writing.
But, bottom line, I would wager that the letter gains no relief from the slavery that so many Chinese suffer - particularly huge numbers of Christian Chinese.
I believe it's authentic. Those who don't are dramatically under estimating Western Culture's influence in China, Japan, Thailand, etc.. Many grow up learning English as a second language due to our media, movies, etc..
I also think once that letter goes public there's a whole factory in for a world of punishment from the Chinese Government. Most here in the U.S. don't realize that the Chinese Government believes the Chinese people are property of the State. Sadly, many Chinese have resigned themselves to that.