Servers cut off your messages, not mIRC. mIRC 7.x just automatically splits your long messages. There are "cut scripts" out there that will do that for you in 6.35 and older.
As long as the server supports unicode channel names and nicks, a channel can very easily move to a unicode version of the channel and use unicode nicks. It doesn't take much to do and considering unicode is where everything is going these days and code page support is being dropped left and right, it's better to make the switch now before someone comes along and creates the unicode version of the channel name preventing you from getting it. If the server doesn't support unicode at all, then you're simply going to be stuck on 6.35 until you either choose another server or else the server makes the effort to support unicode. Unicode has been around for a very long time. At this point, there really isn't a good reason for anyone to not support it yet besides being lazy (talking about servers who don't support it and not the users who can't use it because it isn't supported by the server). I mean, in a decade, they can't manage to support it?