Punctuation missing from system font when Chinese language is selected

Dear experts,

I get glyphs from the system font using CTFontGetGlyphsForCharacters, something like this:

UIFont* uifont = [UIFont monospacedDigitSystemFontOfSize: s weight: w];
CTFontRef font = (__bridge CTFontRef)uifont;
CTFontGetGlyphsForCharacters(font, ....);

The characters that I ask for are basically latin-1 plus a few others.

The app is not localised for Chinese. When I change the phone's default language to Chinese, this code gets glyphs for most characters OK but it fails for a few punctuation symbols:

91 = [
93 = ]
183 = middle dot
8220 = left double curly quote
8221 = right double curly quote

Can anyone guess what's going on here? What's special about those characters?

Thanks, Phil.