But they do work for things posted from IRC.

This is MC-30864, a vanilla bug. EiraIRC currently only fixes this issue for things from IRC chat or when installed on the server.

I probably have a simple way to make it work (and by make it work I mean fix the vanilla bug) on the client-side only for Minecraft chat, might look into that again.

Actually, I just saw this should have been fixed by Minecraft Forge already.

Gonna have to check if something on EiraIRC's client-side is breaking it or if your server owner is just super out of date on Forge.

Just tested on a server on Forge 10.13.3.1408 with no mods and a client with only EiraIRC and I could click links fine, even without the hacky fix I unnecessarily made.

Either your server's Forge version is way out of date or you have some other mod installed that's breaking links.

Hey, you said you had asielib installed, right?

There's your culprit. Unless I've missed something in their code, they're breaking links.