how to trash WordPress comments if its not in English

I don’t think it’s a good idea to trash a comment just because it’s in Russian. I’d recommend using Akisment to prevent/stop spam comments instead of deleting them. Prevention is always better than cure.

If you still want to delete Russian (non-English) comments, add this code to the functions.php file of your (child) theme.

function wpse425768_trash_non_english_comments( $comment_id ) {
    $comment = get_comment( $comment_id );
    $comment_content = $comment->comment_content;

    // Function to detect if the comment is mostly non-English
    if ( wpse425768_is_non_english( $comment_content ) ) {
        wp_trash_comment( $comment_id );
    }
}

function wpse425768_is_non_english( $text ) {
    // Count the number of Latin characters
    $latin_count = preg_match_all( '/[a-zA-Z]/', $text );

    // Count the number of non-Latin characters
    $non_latin_count = preg_match_all( '/[^\x00-\x7F]/', $text );

    // If there are more non-Latin characters than Latin characters, it's likely non-English
    return $non_latin_count > $latin_count;
}

add_action( 'comment_post', 'wpse425768_trash_non_english_comments', 20, 1 );