fromsly samtto The Flarum team is aware of issues regarding UTF8 support inside of Flarum and have active issues on Github for it. As for support for WeChat, Sharing, etc. these will all have to come from extensions, the core extensions are strictly for the general operation of Flarum in general and the OAuth extensions (Github, Facebook, Twitter) are mostly as examples for other developers wanting to implement integration based on my limited knowledge.
The other thing that no one of the Flarum team can anticipate is changes to the way Chinese networks work as none of the team is from China and to put it as nicely as possible it's very unusual for someone to VPN into China, normally people VPN out of China and based on some research there are no mainstream VPN providers that provide a connection into China.
Further Google, Bing and Yahoo can all index Flarum forums just fine which raises many questions about what about Baidu makes it un-indexable. If Baidu has a custom web rendering engine that does not conform to other web rendering engines or lacks a feature that Flarum uses it could potentially cause major issues. As for why that Vivaldi forum renders just fine I'm not sure exactly why, but this would require much more research.