search slug with Chines characters

That’s just spam. It’s not related to Relevanssi, you’d get that without Relevanssi.

It’s relatively harmless. It’s also so common that I happen to have a bit of code that will block those searches:

add_filter( 'pre_get_posts', 'rlv_block_search' );
function rlv_block_search( $query ) {
    if (!empty($query->query_vars['s'])) {
        $blacklist = array( '大奖', 'q82' ); // you can add blacklist entries here; no need for whole words, use the smallest part you can
        foreach( $blacklist as $term ) {
            if( mb_stripos( $query->query_vars['s'], $term ) !== false ) exit();
        }
     }
}

However, it would be even better if those spam searches could be blocked at server level before they even fire up WordPress in the first place.