Disallowed characters in URL and search

[eluser]victorche[/eluser]
These days I will work with this search. So ... My final question about this is simple:
How can I avoid this "disallowed characters" feature at all?

I thought and thought about it. Any search, leading to a 404 page is just not acceptable for me. The search string will be validated anyway, so I really want to avoid this whole feature. I want anything which user types, to go in the url. I thought about adding stuff in allowed chars list. But this seems impossible. I would like to add all cyrilic letters, latin letters like ö,ü ... Seems like a really long list.

So simple question: how can I avoid this thing at all?