That means that the svg-tags 
   font-face, font-face-uri and font-face-src 
can't be used in embedding svg in the "fo:instream-foreign-object" tag.

Solution: In the method setupSVG of the SVGElementMapping class add the following 
lines:
...
   foObjs.put("text", SVGObj.maker("text"));
...
			foObjs.put("font-face", SVGObj.maker("font-face"));
   foObjs.put("font-face-uri", SVGObj.maker("font-face-uri"));
   foObjs.put("font-face-src", SVGObj.maker("font-face-src"));
...

After that you can use font-face and the other tags to change the fonts used by the svg 
object.