This is why mIRC has basic support for accessing these channels with /raw -n
This won't work. Since I have around of 10 different script that are programmed not to interfer each other, I have to change every of this script. And I think it would be the same with other users.
You are correct if you say, we can use raw -n to send iso-characters. But and event in any script must be catched and translated to own script that uses iso-characters. And in situations without user-interaction (i.e. the autojoin-list in many nickserv-implementations), I have no chance to detect the charset.
The only way to solve this would be a kind of low-level-events that cannot be overridden and used to translate between the charsets. But this translation should be the part of the client, not of any user-script.
As I said before, if it is possible to create an inconsistent state, the client has an error - not the user or the server. Nettalk for example hides any iso-channels when I enables utf-8-support. That's not what I excpect, but it's better than an inconsistent state and - that's the point - I have the choice to enable or disable it.