1. Open the file in the koi8-r, koi8-u or cp1251 coding.
2. Gimp say "Opening
'file:///home/dmi/%E9%CD%D1%20%CE%C1%20%D2%D5%D3%D3%CB%CF%CD%20%D1%DA%D9%CB%C5.jpg' 
failed"

This is new Glib problem. Look the description:
Notes about GLib-2.4.0
======================
                                                                               
                                            
* g_filename_to_uri() used to operate like this:
                                                                               
                                            
        1. convert the filename from G_FILENAME_ENCODING to UTF-8
        2. encode the UTF-8 into hexadecimal escapes for URIs
                                                                               
                                            
  This was incorrect, and now the filename is simply escaped for
  conversion into URIs.  g_filename_from_uri() is fixed in the same
  fashion.  Programs which store the converted URIs or filenames may
  need manual conversion.