I have a problem with forum title translate and characters in urls.

1. I see that this forum have this same problem it can to resolve?

Oferta sprzedaży domeny xxxx.pl (xxxx)
must be:
Oferta sprzedaży domeny xxxx.pl (xxxx)

2.
When i log in, non-english characters works fine and polish words are replacement example: ą->a.
Unfortunately guests have a deleted polish words so vbet have a bad links.
How to resolve this?

After login:
Oferta sprzedaży domeny xxxx.pl (xxxx)

Guests:
http://www.carcode.pl/filtry-cz-stek-sta-ych/