While testing complex text I came across a serious problem:

In the FallbackResources, for Mac, the paths for the file fonts are mixed of paths and URL, see T2KFontFactory#getLinkedFonts()
if (isMacOSX) {
    // Hotkey implementation of fallback font on Mac
    fontRegInfo[0].add("file:///Library/Fonts/Arial%20Unicode.ttf");
    fontRegInfo[1].add("Arial Unicode MS");
    
    // Add Lucida Sans Regular to Mac OS X fallback list
    fontRegInfo[0].add(jreFontDir + jreDefaultFontFile);
    fontRegInfo[1].add(jreDefaultFont);
                
    // Add Apple Symbols to Mac OS X fallback list
    fontRegInfo[0].add("file:///System/Library/Fonts/Apple%20Symbols.ttf");
    fontRegInfo[1].add("Apple Symbols");
    
    return fontRegInfo;
}

Note that the first and last are URL, the second is path.

Try to use this text+font in a Text node:
Text node = new Text("\u0625\u0626 \u0627\u0628");
node.setFont("System", 36);

running with -Dprism.debugfonts=true I get the exception:
java.io.FileNotFoundException: Unable to create FontResource for file file:///Library/Fonts/Arial%20Unicode.ttf
at com.sun.t2k.T2KFontFile.init(T2KFontFile.java:539)
at com.sun.t2k.T2KFontFile.<init>(T2KFontFile.java:186)
at com.sun.t2k.T2KFontFile.createFontResource(T2KFontFile.java:112)
at com.sun.t2k.T2KFontFile.createFontResource(T2KFontFile.java:174)
at com.sun.t2k.T2KFontFile.createFontResource(T2KFontFile.java:127)
at com.sun.t2k.T2KFontFactory.getFontResource(T2KFontFactory.java:438)
at com.sun.t2k.FallbackResource.getSlotResource(FallbackResource.java:195)
at com.sun.t2k.T2KCompositeFontResource.getSlotResource(T2KCompositeFontResource.java:53)


that is because createFontResource expects to be called with a path not a URL.

Either, this has be broken for a long time (which is bad), and surprising since we touched this code recently with RT-20718.
Or I broke it implementing dfont/woff (but as far as I can tell this has being broken before me).