This is probably not a viable answer, but I'll post it anyway in case it's of interest.
The Roslyn compiler is open source, so it can be modified, and in this way the error messages can be changed from English to French, or whatever. Just be aware that Roslyn is a huge program, and rebuilding it is not all that easy, at least in my experience.
I've written a few blog articles about my experiences with modifying Roslyn. My latest modification included adding a new error message - that's how I happened to find this question.
https://renniestechblog.com/information/33-modifying-roslyn-step-1-initial-test
https://renniestechblog.com/information/39-modifying-roslyn-step-6-fake-attribute-yacksserialization
It may even be possible to make Roslyn multilingual, by adding an additional CSharpResources.fr-FR.resx
file to the project, and letting ResourceManager
automatically choose the correct .resx file. This definitely works with .Net Framework WinForms projects, but I don't know if this functionality has been preserved in the new .Net Standard format.