I use the UK-Extended keymap as it allows easy typing of all the following characters: áéíóúẃýàèìòùẁỳäëïöüẅÿâêîôûŵŷãõç
Ability to type these characters is important as I enjoy creating languages (conlanging) and often need these symbols.
However, when inputting these characters into mIRC the following characters appear as question marks, rather than the correct symbols: ẅẃẁỳ
The result is that I must paste these symbols in from another place such as Notepad, which is a hassle.
(It appears not even the forum software here is capable of handling Unicode correctly; you may need to paste the character codes into another Web page to view them.)