You can always insert the Turkish Lira symbol in the editor from code. The following code-snippet illustrate how to achieve this:
As to the InsertSymbolDialog, it actually shows the symbols of all fonts registered on the machine, so if you select a font which contains the symbol in the drop-down you should be able to insert the symbol. Also, if you register a custom font containing this symbol it should be picked-up by the dialog. Here is how a custom font can be registered:
FontFamilyInfo fontFamilyInfo = new FontFamilyInfo(new FontFamily(familyName), "My Custom Font Name");
Let me know if I can assist you with anything else.
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