Onni Hakala

Geniem Oy

WordPress plugin which removes all accented characters like <code>åöä</code> from future uploads and has easy wp-cli command for removing accents from current uploads and attachment links from database. 
This helps tremendously with current and future migrations of your site and helps you to avoid strange filename encoding bugs.
Sanitize accents from Cyrillic, German, French, Polish, Spanish, Hungarian, Czech, Greek, Swedish. 
This even removes rare but possible unicode NFD characters from files by using <a href="http://php.net/manual/en/normalizer.normalize.php" rel="nofollow ugc">PHP Normalizer class</a>. These usually happen if you have mounted uploads into your vagrant box in OS-X.
This plugin is wordpress multisite compatible.
More information in github page: https://github.com/devgeniem/wp-sanitize-accented-uploads

WP Sanitize Accented Uploads

Simple plugin which removes accented characters from uploaded files.

Nikolaos Anastopoulos

This plugin operates transparently, always loading the homonymous jQuery script that automatically replaces uppercase accented characters. The script operates automatically on the document ready event, by selecting all the elements having their text content uppercase transformed through CSS, and by replacing the accented characters in them by their respective non-accented.
Currently the script upstream supports only greek text. Plugin versioning follows upstream versions.

jQuery Remove Uppercase Accents

Automatically replaces accented characters (currently greek) from elements having their text content uppercase transformed through CSS.

WP Sanitize Accented Uploads vs jQuery Remove Uppercase Accents