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.

devoutpro

NoMore404 is a free WordPress plugin for redirection of 404 pages and simple firewall to block malicious hosts and URLs. 
All redirections are done via 301 redirection. 
You can mark any hosts and URLs to be blocked as malicious as well.

Nomore404 404 Redirection and Firewall

NoMore404 is a free WordPress plugin for redirection of 404 pages and simple firewall to block malicious hosts and URLs.

Permalink Encoding vs Nomore404 404 Redirection and Firewall