imo the description has to be made better. yesterday i lost a lot of time trying to figure out how this actually works.
something like this:
you MUST have a font installed (not only the symbol font!)
you MUST have a language file (right?)
these two MUST be selected in the CHDK options.
after that, you can enable symbol mod and choose the symbol font (preferably same size as system font).
perhaps you should incorporate some checks like "if no custom font loaded, disable symbol mod".?