mplayer & UTF-8 locales

[R.I.P.]

Hi,

I'm using locale en_US.UTF-8 and I want to watch a video with russian subtitles in cp1251 encoding
Hence I'm starting "mplayer -subcp cp1251 somevideo.avi" and it doesn't work - I see underscores instead of letters.
The strange situation is that in locale ru_RU.UTF-8 same command works fine.

I've always thought that unicode locales shouldn't behave differently with the stuff related to the encodings and that the only difference is stuff like date&time format and language of the messages. Am I wrong?