Run this file with wp-cli: $ wp eval-file remove-accents-uploaded-files-and-database.php to remove accents from all of your previous uploads. Also fix OS-X NFD filenames. After running this command install https://gist.github.com/onnimonni/d58bdcff44f8208a15c7 to your mu-plugins to avoid this in future uploads.

remove-accents-uploaded-files-and-database.php

<?php
/**
 * Sanitize accents from Cyrillic, German, French, Polish, Spanish, Hungarian, Czech, Greek, Swedish
 * This replaces all accents from your uploads by renaming files and replacing attachment urls from database.
 * This even removes NFD characters from OS-X by using Normalizer::normalize()
 * This is one time script which you can use by running it with wp-cli:
 * $ wp eval-file remove-accents-uploaded-files-and-database.php
 */

// Get all uploads
$uploads = get_posts(array(
  'post_type'   => 'attachment',
  'numberposts' => -1,
));

function onnimonni_sanitize_accents($string) {
  # If available remove NFD characters
  if(class_exists('Normalizer')) {
    $ascii_string = remove_accents(Normalizer::normalize($string));
  } else {
    $ascii_string = remove_accents($string);
  }
  return $ascii_string;
}

// Replace mysql later
global $wpdb;

// Get upload path
$path = wp_upload_dir()['basedir'];

echo "Found: ".count($uploads)." attachments...\n\n";
echo "This may take a while...\n";
foreach ($uploads as $upload) {
  echo "Processing upload (ID:".$upload->ID."): {$upload->guid}";

  if (! is_array($upload->$guid) ) {
    echo "\nskipping {$upload->post_title}...\n";
  }

  foreach ($upload->$guid["_wp_attached_file"] as $index => $file) {

    $full_path = $path.'/'.$file;
    
    $ascii_file = onnimonni_sanitize_accents($file);

    $ascii_guid = onnimonni_sanitize_accents($upload->guid);
    
    $ascii_full_path = $path.'/'.$ascii_file;
    // This replaces main file
    if ( $file != $ascii_file || $ascii_guid != $upload->guid ) {
      echo " ---> Replacing to: {$ascii_full_path}\n";

      # Move the file
      rename($full_path, $ascii_full_path);

      # Replace thumbnails too
      $file_path = dirname($full_path);
      $metadata = unserialize($upload->$guid['_wp_attachment_metadata'][$index]);

      // Correct main file
      $metadata['file'] = $ascii_file;

      // Usually this is image but if this is document instead it won't have different sizes
      if (isset($metadata['sizes'])) {
        foreach ($metadata['sizes'] as $name => $thumbnail) {
          $metadata['sizes'][$name]['file'];
          $thumbnail_path = $file_path.'/'.$thumbnail['file'];

          $ascii_thumbnail = onnimonni_sanitize_accents($thumbnail['file']);

          // Update metadata on thumbnail so we can push it back to database
          $metadata['sizes'][$name]['file'] = $ascii_thumbnail;

          $ascii_thumbnail_path = $file_path.'/'.$ascii_thumbnail;
          echo "Processing thumbnail: {$thumbnail_path} ---> {$ascii_thumbnail_path}\n";          
          rename($thumbnail_path, $ascii_thumbnail_path);
        }
      }

      $fixed_metadata = serialize($metadata);

      ##
      # Replace Database
      ##

      ## Replacing guid
      echo "Replacing attachment guid in database...\n";
      $sql = $wpdb->prepare("UPDATE {$wpdb->prefix}posts SET guid = %s WHERE ID=%d;",$ascii_guid,$upload->ID);
      $wpdb->query($sql);

      ## Replace upload name
      echo "Replacing file name in database...\n";
      $sql = $wpdb->prepare("UPDATE {$wpdb->prefix}postmeta SET meta_value = %s WHERE post_id=%d and meta_key='_wp_attached_file';",$ascii_file,$upload->ID);
      $wpdb->query($sql);

      ## Replace meta data likethumbnail fields
      echo "Replacing thumbnail names in database...\n";
      $sql = $wpdb->prepare("UPDATE {$wpdb->prefix}postmeta SET meta_value = %s WHERE post_id=%d and meta_key='_wp_attachment_metadata';",$fixed_metadata,$upload->ID);
      $wpdb->query($sql);

    } else {
      echo "\n";
    }
  }
}