WordPress functions dependent on the https://github.com/Automattic/WPCOM-Legacy-Redirector plugin

fix-urls-with-special-characters.php

<?php
/**
 * Try to fix broken pre-Drupal urls with special characters if we have saved their posts
 * @return array $vars
 */
if ( ! function_exists( 'minnpost_largo_special_character_url_redirect' ) ) :
	add_action( 'template_redirect', 'minnpost_largo_special_character_url_redirect' );
	function minnpost_largo_special_character_url_redirect() {
		// check if is a 404 error
		if ( is_404() ) {
			$option    = 'minnpost_urls_to_redirect';
			$full      = $_SERVER['REQUEST_URI'];
			$requested = basename( parse_url( $_SERVER['REQUEST_URI'], PHP_URL_PATH ) );
			$fixed     = sanitize_title( $requested );
			// check if the URL changes when it gets WordPress-sanitized
			if ( $requested !== $fixed ) {
				$replaced = str_replace( $requested, $fixed, $full );
				if ( class_exists( 'WPCOM_Legacy_Redirector' ) ) {
					$urls     = get_option( $option, array() );
					$this_url = array(
						'from'       => $full,
						'to'         => site_url( $replaced ),
						'redirected' => false,
						'updated'    => false,
					);
					$urls[]   = $this_url;
					update_option( $option, $urls, false );
				}
			}
		}
	}
endif;

/**
 * When admin loads, parse any special character redirects and try to create them
 *
 */
if ( ! function_exists( 'minnpost_largo_admin_special_character_url_redirect' ) ) :
	add_action( 'admin_init', 'minnpost_largo_admin_special_character_url_redirect' );
	function minnpost_largo_admin_special_character_url_redirect() {
		if ( is_admin() && class_exists( 'WPCOM_Legacy_Redirector' ) ) {
			$option = 'minnpost_urls_to_redirect';
			$urls   = get_option( $option, array() );
			if ( ! empty( $urls ) ) {
				foreach ( $urls as $key => $url ) {
					if ( ! isset( $url['updated'] ) || ! isset( $url['redirected'] ) ) {
						unset( $urls[ $key ] );
						continue;
					}
					$redirect_inserted = false;
					$post_updated      = 0;
					if ( true !== $url['updated'] ) {
						$post_name = urldecode( basename( parse_url( $url['from'], PHP_URL_PATH ) ) );
						global $wpdb;
						$posts = $wpdb->get_results( 'SELECT ID FROM ' . $wpdb->prefix . 'posts' . ' WHERE post_name = "' . $post_name . '"', ARRAY_A );
						if ( empty( $posts ) ) {
							continue;
						}
						$post    = $posts[0];
						$post_id = $post['ID'];
						$post_updated = wp_update_post(
							array(
								'ID'        => $post_id,
								'post_name' => basename( parse_url( $url['to'], PHP_URL_PATH ) ),
							)
						);
						if ( 0 !== $post_updated ) {
							$url['updated'] = true;
						}
					}
					if ( true !== $url['redirected'] ) {
						$redirect_inserted = WPCOM_Legacy_Redirector::insert_legacy_redirect( $url['from'], $url['to'] );
						if ( true === filter_var( $redirect_inserted, FILTER_VALIDATE_BOOLEAN ) ) {
							$url['redirected'] = true;
						}
					}
					$urls[ $key ] = $url;
					if ( true === filter_var( $redirect_inserted, FILTER_VALIDATE_BOOLEAN ) && 0 !== $post_updated ) {
						unset( $urls[ $key ] );
					}
				}
				update_option( $option, $urls, false );
			} else {
				return;
			}
		}
	}
endif;