shows the standard unicode box.
Presumably this is because the syriac fonts
are installed in /usr/X11R6/lib/X11/fonts/OTF,
which isn't referenced in the fontconfig config file.
Well, sort of. Note that even if the fonts are added, Syriac won't
render properly in GNOME (would need a couple of days work within
Pango) or probably KDE. (It's conceivable that Qt has support for
Syriac, but I doubt it.)
This was fixed in 2.1.2-6 a while ago.