Claudia is right about it : your present version of the Monaco font cannot reproduce the glyph of the character ổ ( “LATIN SMALL LETTER O WITH CIRCUMFLEX AND HOOK ABOVE”, of Unicode code-point 1ED5 )

This character is part of the Unicode Latin Extended Additional block, which describe 256 characters, from Unicode code-point 1E00 to Unicode code-point 1EFF. Refer to the link, below, to get the complete list of these characters

http://www.unicode.org/charts/PDF/U1E00.pdf

Now, I found out, a nice monospaced font, named Monaco for Powerline, with Euro sign and slashed zero, proposed by Daniel Shæfer ( alias epegzz ), which works on Windows configurations and, probably, on OSX ones ! You can download it from the link, below :

https://gist.github.com/epegzz/1634235/raw/4691e901750591f9cab0b4ae8b7c0731ebf28cce/Monaco_Linux-Powerline.ttf

Consult, also, the page :

https://gist.github.com/epegzz/

Once this font installed, on your operating system, your text chào buổi sáng should be correctly displayed :-))

Only 10 characters, ( from 1E9C to 1E9F and from 1EFA to 1EFF ), out of the 256 characters, of the Latin Extended Additional block, do not have any glyph, with the Monaco for Powerline font. These are, principally, some medieval characters + the Latin Capital German letter Sharp S, of code 1E9E

Hope this post will help you !

Best Regards,

guy038

so it looks like this font (Monaco) doesn’t support all glyphs.

Cheers
Claudia