Manual:$wgSVGConverterPath/de-formal

Details
By default, when invoking a SVG converter, MediaWiki simply passes a command line such as, leaving it up to the operating system to locate the executable.

If your chosen SVG converter is not in the executable PATH, MediaWiki will not find it. In this case, you need to use this setting to specify the directory in which the SVG converter is located.

You will almost certainly need to set this variable on Windows systems.

Example
This will use the converter from inside the  directory: