Suggestion: add a property AdditionalLicenses of type PropertyMap and extend the class DlgProjectInformationImp accordingly.

Can I work on this feature?

Sure.

In order to be backward compatible I recommend to add a new property of type App::PropertyStringList. The name of the property can be AdditionalLicences, FurtherLicenses, MultiLicense, ... or something like that and will be filled if more than one license is used.

The currently used property License must not be changed or removed as otherwise older FreeCAD versions won't be able to show the correct license of files created with a newer version.

Then DlgProjectInformationImp should be extended to conveniently set additional licenses

@wwmayer Which file should be modified to add the feature?

src/App/Document.cpp and .h

Can I ask in what kind of scenario would someone want multiple license per file?

The request came from the German sub-forum. The issue is that some OSS licenses are not compatible with each other and then it might be helpful to have a file dual-licensed.

I'm currently working on the issue. Should I also design the UI part? or just the backend part is sufficient?

ping @hashoak