If LANG=ru_RU.KOI8-R, the Cyrillic characters on the input line are garbled. I applied a patch from https://github.com/irssi/irssi/issues/1018 to the port and it fixed the problem.
Created attachment 205097 [details] Patch from https://github.com/irssi/irssi/issues/1018 I have tested it and it works for me in KOI8-R locale.
*** This bug has been marked as a duplicate of bug 238591 ***