The Chinese server is very still alive, actually. It was just down temporarily due to domain issues. I was playing like last week actually.
As for the English server, that's a bit of a mess... There's actually a few different projects going, and various Discord servers for them, but there has apparently been some drama involved. If you're interested in the English private server, there is one playable, kind of, under the name Re:IMAGINE, though the server is being remade from scratch and is very glitch-y, and ironically isn't currently in English from what I have seen.
The English server is still in progress but is more up-to-date. Also it's in Japanese.
The Chinese server is using an outdated version of the game, but is mostly functional, and can be played in English.
Point is, the English server might be fun to play to keep up with things and experience it as it develops, but the Chinese server is more complete and playable, and at the moment, my preferred method to play.
(edited by Hibiki)