Didn’t find any guide or tip how to enable joins/parts in Weechat for Twitch’s IRC server, here’s how to do it in Weechat!
I have the server saved with the alias “Twitch”, the command might vary a bit for you:
/set irc.server.Twitch.command "/quote CAP REQ :twitch.tv/membership"
Now reconnect to the IRC server and you should see something like this:
Twitch -- | irc: connecting to server irc.twitch.tv/6667...
Twitch -- | irc: connected to irc.twitch.tv/6667
Twitch -- | irc: client capability, enabled: twitch.tv/membership