I'd like to give some suggestions to improve it

1) Options: I don't like the language menu.
I suggest you to use a drop-down menu.
If you still want to show the flags, use a little icon instead of those BIG icons.
2) Options: You could add new items in the future, can't you?
Here too it could be useful a list with scrollbars and checkboxes
3) Give your users the possibility to insert new folders and/or files to be deleted completely
4) Give your users the possibility to export the log of found items
5) Give your users the possibility to have a log file created automatically after they used the program (in the log folder of your program), or after the automatic mode did for them
6) Give your users the possibility to first move the files in the recycle bin
7) Give your users the possibility to ignore files and/or folders
8) When the portable version is used, put all the files in the KCleaner folder