While working on French documents, I sometimes need to extract some parts to turn them in a more neutral form. Like turning an article title with accents into a filename or a slug for a URL.
So to remove diacritics from a selection le garçon hérétique → le garcon heretique, I use the filter command | with iconv
define-command to-ascii %{
execute-keys '|iconv -f utf8 -t ascii//TRANSLIT<ret>'
}
Beware, for some characters it can expand selections, like in German with ß replaced by ss.