VFP does not support Unicode natively. If you need to display Unicode characters then you need some conversion and appropriate font to display the results. But this you probably know.
Questionmarks are caused either by impossible conversion or by font which does not support such characters. Both font and conversion routine is provided by operating system and VFP has no influence on it. If the character is displayed correctly in Unicode enabled software then the most probably reason is conversion. You should test you app on newer OS (Vista, W7) with chinese support installed.
Sorry I cannot help more.
Rick Strahl published interesting paper about Unicode in VFP on his web:
http://www.west-wind.com/presentations/foxunicode/foxunicode.aspThis discussion could give you more info (and see links at the end):
http://www.foxite.com/archives/how-to-implement-unicode-in-vfp-0000208914.htmThis link worked for me from Google cache:
http://209.85.135.132/search?q=cache:c28XJBaXzswJ:www.programmersheaven.com/2/using-unicode-in-visual-foxpro+chinese+in+foxpro&cd=9&hl=cs&ct=clnk&gl=cz