As mentioned above, this is because mIRC is now a Unicode application and will only send and receive UTF-8 encoded text. The purpose is to, ideally, make IRC as a whole non-reliant on codepages, so that everyone will be able to view all characters in all languages. In older versions of mIRC, every user had to manually configure each of their channel/query windows with a specific font and codepage to display one particular language, and this only worked for that language, so if someone new joined the channel, or someone joined that channel and spoke a different language, text would appear as garbage to them and to others. The use of UTF-8 means that none of that is necessary any more. Everyone on IRC will be able to read everyone else's text, regardless of language, without any fiddling or confguring codepages. You can find discussions on this issue
here,
here and
here.
