groff does it with the help of its preconv(1), also invoked with groff's -k option.

    $ printf 'Hello ①②③\n' | preconv
    .lf 1 -
    Hello \[u2460]\[u2461]\[u2462]
    $ printf 'Hello ①②③\n' | groff -k -Tutf8 | grep .
    Hello ①②③
    $