PHP code structure for string manipulation tasks
Yes, I think your variable names are a bit long.  While it is good to be expressive, you don't want to be pushing your line width beyond the recommended max width if avoidable.

I don't know if you need many custom functions here.  The shared calls which filter empty and duplicate strings can be a custom call.  Otherwise, everything else is single-use.

Consider this snippet which simplifies much of the script by grouping the multibyte and single-byte non-whitespace substrings from the start.  No extra exploding, and only one implode call.

Code: (Demo)

function uniqueNoEmpty($array) {
    return array_unique(array_filter($array, 'strlen'));
}

$original_string = 'one two three 喞 喝 four 刷囿 two 跏正 吁';

if (!preg_match_all('~(\p{Han}+)|(\S+)~u', $original_string, $out)) {
    echo 'no qualifying strings';
} else {
    $singleBytes = uniqueNoEmpty($out[2]) ?? [];
    $multiBytes = array_reverse(uniqueNoEmpty($out[1]));

    echo implode(' ', array_merge($singleBytes, $multiBytes));
}