Ok, seems that
WeeChat has got almost all features I used in irssi so none is missing except from lastlog. This isn't implemented yet but the development of WeeChat is active.
For people who are new to weechat maybe the option:
set irc_dislay_away=off is important because it prevents weechat from sending public away messages which
are not welcome in almost every irc channels.
Another thing is that I discovered a segfault in the source code of weechat. The command line argument length isn't
checked so if you use an argument with a huge length it will crash.
I mailed this bug to the upstream source and hopefully they will fix it soon.