Template:Package Official is available in the [extra] repo. Install by running:
# pacman -S weechat
WeeChat is going to have multiple interfaces at some point, run weechat-[interface] to start WeeChat.
As WeeChat currently only has a Ncurses interface the command to start WeeChat is:
If you're making a server with /server add -ssl to the end of the line, for example:
/server add FreenodeSSL chat.freenode.net/7000 -ssl
You can do the same thing if using /connect.
/connect chat.freenode.net/7000 -ssl