Hi,
This is somewhat tricky due to the way encoding is handled on the VisualGDB side. We might be able to look into supporting it during the next major VisualGDB release, however it would take more than several months.
As a workaround, we would advise creating a wrapper for the external tool that would run the original tool, and then change the encoding of the generated file to UTF-8. As it will be done automatically each time after the tool is invoked, it won’t result in any extra changes in git. From the source control point of view, it will look as if the tool was generating UTF-8 files in the first place.