I support Unicode. I barely read and write cyrillic but I do believe that not allowing it (and other non-Roman characters) won't stop people from writing on their own language in general channels, they will just use a transcription for it. Only respect towards the others on the server can help in this matter.
I played on an international server, we had people from the UK, Germany, Spain, Portugal, Italy, Poland, the Czech Republic, Hungary, the Netherlands, Russia etc. and everybody were speaking English just because that was the language all of us understood.