I have some old permalinks (posts, pages, tags) that contain now-illegal characters in them – and these aren’t working anymore.
In previous versions of WP it was allowed to use the non-latin characters, but that changed in newer versions.
Is there any way to clean the database from these permalinks (converting them to allowed format)?
This plugin should allow you to do that http://wordpress.org/extend/plugins/wp-utf8-sanitize/