Let’s be honest for a second, the Irssi nick completion sucks. In particular, it does not feature “partial” completion like BitchX or your favourite shell might.
I found a script called niq on the “official” scripts page which promised to relieve this shortcoming, but for some reason it wouldn’t work.
So one day when I was muttering about this in the #irssi irc channel, some guy (don’t remember you, sorry! contact me if you want credits.) told me “well yea this is broken and there is a fixed version at this-and-that place.”
And I was like “oh great why did noone ever tell me” — and this is exactly the problem with the central Irssi scripts archive: badly maintained.
I don’t even know what this page was where it had the fixed version, sorry about that. But at least I mirrored the script so hopefully someone will find it here.