Sorry, but there is nothing in texinfo.tex to load Cyrillic fonts, or really anything but ISO Latin 1 and a little of 2 and a tiny number of other characters.
It's a serious deficiency. Maybe the only short term solution is to generate the PDF from the HTML output somehow? (I don't know how, but I suppose it's possible). Also, searching for "cyrillic texinfo.tex" turns up some possible patches from Werner Lemberg and others. I haven't investigated in depth. There used to be a separate texi2latex program (texi2latex.nongnu.org) but it hasn't been updated for some years so likely doesn't work on your source. You could try. Long term, I hope we will have a LaTeX back end in makeinfo. It's not practical to try to support everything in texinfo.tex. (An incomplete attempt is in texinfo/contrib/texifont if any serious TeX hackers get interested, though.) (Also sorry for the delayed reply.) karl
