Use cl-who to create the HTML output, in which a <meta> tag is used to specify UTF8.
From https://github.com/mcandre/doeshunchentootwork/blob/master/doeshunchentootwork.lisp.
(defmacro standard-page ((&key title) &body body)
`(cl-who:with-html-output-to-string (*standard-output* nil :prologue t :indent t)
(:head
(:title ,title)
(:meta :http-equiv "Content-Type" :content "text/html;charset=utf-8"))
(:body :style "text-align: center;"
(:h1 "Does Hunchentoot work?")
,@body))))
Cheers,
Andrew Pennebaker