@Tomao
You need to check if the text is utf-"conform" first, like $iif($isutf($1-),$utfdecode($1-),$1-) - see here

@Tohe
If you enter ā ī or ō in the text editbox, do you "see" these chars in the editbox as they should be (as macrons), or do you see them as â î and ô (with the caret/circumflex)?
(Note that you might need to copy-paste this phrase into mIRC, at least my browser doesn't display the chars utf-encoded here in the forum)

If it's the latter, there's nothing wrong with the UTF-processing of text you send or receive. Instead the input itself isn't interpreted as it should be...