I have a zen cart installation with 2 languages: Hungarian and Romanian. Charsets are set to utf-8, mysql field collations are utf8_general_ci and, in DB characters are ok, and I still get strange question marks instead of language specific characters. I also checked the fonts.
PS: Text that comes from the translation files(not from DB) has diacritics, DB results don't.
Your page is actually running with the following character set definition:
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
change that to UTF-8 and it should work if all the other data is also properly UTF-8 encoded.