Google will use any sub-set of the font it wants. Did you make sure to check the correct boxes when you got the code for it?
When I append <link href='http://fonts.googleapis.com/css?family=Open+Sans:400,600,700,800,300&subset=latin,cyrillic-ext,cyrillic,latin-ext' rel='stylesheet' type='text/css'>
to your <head>
, all the characters look correct.
Just make sure to check whichever sub-sets you need so you don't get unnecessarily large files.