Special characters in URL key string

[Stéphane Miousse]

I noticed that accentuated and special characters are not validated when
entered as a URL key. I know that these characters are not supposed to
be used in a URL path but some people does nevertheless. It could also
be due to a typing error. It generates major problems and errors when
accessing the page in edition. Is there actual or incoming developments
in validating this string to solve this problem?