2) copy CP1251-*, KOI8-R-* directories and 'font' symlink
to ~/.mplayer/ or to the system mplayer directory, usually
/usr/local/share/mplayer/ :
$ cp -r CP1251-* KOI8-R-* font /usr/local/share/mplayer/
3) to set up desired font size/encoding switch the ~/.mplayer/font symlink, i.e.:
$ rm ~/.mplayer/font
$ ln -s CP1251-18 ~/.mplayer/font
or in system directory:
$ rm /usr/local/share/mplayer/font
$ ln -s CP1251-18 /usr/local/share/mplayer/font