How to fix file name encoding

Chances are that if you just decode the %XX URI encodings, you'll get UTF-8 encoded characters. In zsh:

autoload zmv
LC_ALL=C zmv '(**/)(*%*)' '$1${2//(#b)%(??)/${(#):-0x$match}}'

If as noted by Gilles, that � substitution character is for a 0xc3 byte (which in iso8859-1 is a letter which would explain why it hasn't been URI-encoded contrary to 0x9c which is invalid in iso8859-1), then the above command would change your file name to Übersicht.html

After decoding the %XX URI encodings to valid UTF-8, you could also have used convmv -f utf-8 -t latin-1 to convert the character set of the filename.

That might be an useful alternative solution if zsh is not available.