it’s not the problem of locale setting at all.
in mdv 2007’, the default setting on ’fontconfig’ of mplayer.conf in /etc/mplayer/ is yes. however the documentation tells us :
’If MPlayer was compiled with fontconfig support, the above methods
won’t work, instead -font expects a fontconfig font name and defaults
to the sans-serif font. ...’
(
http://www.mplayerhq.hu/DOCS/HTML/en/fonts-osd.html
)
so it’s quite possiblely just the problem of this default setting.
in my own experience,at first i also got lots of following warning:
  Selected font is not scalable. Using ppem=15.
  FT_Set_Pixel_Sizes failed.
  Wrong bounding box, width
  Cannot prepare subtitle font.
even if i had specified the font in the .conf file or in command line.
when i disable the setting of ’fontconfig=yes’ in the .conf ,there is no more ’using ppem=15’ warning at all.
似乎这个问题和fontconfig有关系，vim /etc/mplayer/mplayer.conf，将fontconfig = yes  --->no，现在使用一切正常。