crille

Non-ASCII characters can be used in the URL, but they have to be encoded (RFC3986). URL encoding is widely used (e.g. Wikipedia http://ja.wikipedia.org/wiki/Wikipedia:%E9%80%A3%E7%B5%A1%E5%85%88). 
This plugin encodes NON-ASCII characters in the slugs of your pretty permalinks. So your slugs may look like <code>fußball-in-nürnberg</code> or <code>連絡先</code>.

Permalink Encoding

This plugin encodes NON-ASCII characters in pretty permalinks by using Percent-Encoding described in RFC3986.

Pierre-André Boissinot

Semio Design

When you use the WordPress editor to insert a media in the content field it stores a reference to the absolute path. 
So if you change the location of your site (by switching from staging to production environment for example) all your paths will be incorrect. 
This plugin stores relative pathes in the db instead of an absolute path. 
Beware: this plugin must be activated BEFORE inserting a media into the content field. It has no effect on the medias stored before the activation. 
It’s mostly based on the WP_SITEURL constant which should be defined in the wp_config.php file. If this constant isn’t defined it uses the “siteurl” option value instead. 
If the plugin detects that you access the website from another location than the “siteurl” defined initially it can correct most of the wrong urls in the database.
Localisation of the plugin into french.

Simple Relative Content

This plugin makes all attachments urls stored in database relative to the WP_SITEURL url.

Permalink Encoding vs Simple Relative Content