If the standard fonts of FOP (Helvetica, Times, Courier, Symbol and ZapfDingbats) contains the character, then you do not use additional fonts.
FOP use unicode. So you must insert the unicode value (code point) of the character in your fo file. If you mean with slanted apostrophe the character with the adobe font name quoteright the code point is 2019. This is a hexadezimal value. Using the iso-8859-1 encoding you have to insert the numeric character reference in your fo file, for example: <fo:block font-family="Helvetica">‘text’</fo:block> To find the code point of a character of the Helvetica font, you can search the adobe font name of the character in chapter C.1 of the pdf reference manual http://partners.adobe.com/asn/developer/acrosdk/DOCS/pdfspec.pdf and then use the adobe glyph list http://partners.adobe.com/asn/developer/type/glyphlist.txt Rainer Garus