> Please re-verify that.  Maybe it's your mailer that did some recoding,
   > in which case please send the files as a compressed archive.

As Lars pointed out, gnus converted them to UTF8.

I just resent them as recommended
  > Try renaming the file to document.bin and resend it as octet-stream...


As I said I convert the original files with 


iconv -f ISO8859-8 -t UTF-8 old.txt > new.txt

And the new one emacs displays perfectly. So I conclude the old ones
were in iso8859-8 encoding.