Where on Earth did you find that?! Strange there’s been no official announcement about it that I can find!
But anyway, to answer your questions until the affiliate team respond (which will probably be tomorrow now)…
Needs to be a blog post. So although you can post links to the blog post in forums, other creative platforms and freelance worker platforms, they’d be unlikely to qualify as being ‘a blog post’. Like if you wrote up your post here, and posted it in the Envato forum… that’s not a blog post. However, there are plenty of free blogging sites out there that don’t require you to have your own website.
There’s nothing in the rules that say your post needs to be in English, so unless we get clarification to the contrary, writing your post in Chinese is fine. However, keep in mind that the majority of people judging the contest will probably have English as a first language. Well, a strange version of English. I’m going to assume that very few, if any, of the judges will be able to read Chinese. That means they’re probably going to have to judge your entry using Google Translate… and a lot may be lost in the translation. So I wouldn’t recommend it.
It says search results in the US, so it’s unlikely you’ll be able to test unless you have some kind of VPN based in the US… or there’s some way to test results from different locations that I don’t know about.
Keep in mind my answers are based on an interpretation of the information provided, and may vary from the official answers you’ll probably get at some point.