Weechat
Weechat is a ncurses based IRC client. It currently does not support assigning a CA on a per per-network basis, so you might need to add the Let's Encrypt root certificate to your certificate store. If you have a separate certificate store, you'll probably know how to do this. If you don't, no further steps are required.
Then, to connect:
/server add xinutec irc.xinutec.net/6697 -ssl
There are more flags than
-ssl, most importantly also
-autoconnect. See
/help server for more information.
Finally, connect the newly created server:
/connect xinutec
See you there!