Fontconfig error: Cannot load default config file

I got this error when starting a GTK+ application:

Fontconfig error: Cannot load default config file

It means that the fonts.conf file can't be found by Fontconfig. A fonts.conf file has to be installed in the C:\WINDOWS directory (or anywhere really). Then open regedit and add a couple of keys.

Windows:

$ regedit

Wine:

$ wine regedit

Open: HKEY_CURRENT_USER\Environment

Add the keys:

FONTCONFIG_FILE => C:\WINDOWS\font.conf
FONTCONFIG_PATH => C:\WINDOWS

The fonts.conf file is an XML-document, it should look something like this on windows:

    C:\WINDOWS\fonts
    C:\WINDOWS\Cache\Fontcache
    C:\WINDOWS\Cache\Fontcache

    
    Z:\usr\share\fonts
    Z:\usr\local\share\fonts
    Z:\usr\X11R6\lib\X11\fonts