One of the BackupPC systems of file restore is a TAR archive. The problem is I can get those TAR archive extracted correcty in Linux only. In Windows enviroment 7Zip does not detect polish national characters correctly.

Is there any better extractor with national character support?

I can only suspect the TAR files I'm dealing with are coded in UTF8.

You could try the unixutils native w32 port or the cygwin port. I never tried them on a w9x though so i don't know if they will work.

There is the djgpp version and if you need an up to date mingw port, it will most likely be on the mingw web site.