You see, when they type #ö in old mIRC, they join one channel, if they type #ö in new mIRC, they join another channel, and if they type #Ö they join a third channel, none of these channels are the same.
Or, the channel owners can move their channel to a valid UTF8 name in all lowercase and then everyone can upgrade and use the channel without problem. The first and second #ö you listed are different because the first one isn't valid UTF8. If the channel owner just registers the channel as UTF8 and leaves it as lowercase (since most people joining a channel will type the channel in lowercase), that will solve the problems. In fact, anyone with older versions of mIRC could still access that channel after the change as long as they have UTF8 enabled in options.
Again, mIRC isn't changing. Networks and ircds aren't going to change very soon. If channel owners care at all about having their channels set up so that the highest number of people can access them without problem, they should move the channels to valid UTF8 channel names. Sure, it's a pain to move a channel. I've done so multiple times. But it's not the end of the world and it is by far the better option rather than maintaining the channel in non-UTF8. Many people want to update to the latest version of mIRC and, in the end, many will just stop visiting any channel they can't access after updating rather than trying to make it work. Any decent channel owner should understand this and make the effort. Even when networks add support for UTF8, there is a good chance they'll still allow the outdated channel names and you'll still be in the same situation. Better to change now than later.
All major clients support UTF8 channel names and even older mIRC versions will if set up properly (though people should just update anyhow), so changing the channel name to valid UTF8 makes the channel available to virtually everyone, whereas leaving it in non-UTF8 makes it unavailable to a large number of users. Again, any channel owner who cares at all about the channel should understand this and make the effort to change. It only benefits them to do so.
