Can't determine project language from files

When F5 debugging in Visual Studio 2019, I get multiple warnings from the CLI tools not being able to determine the project language, but the function is hosted locally with no issues and can be triggered, but the `Hosting Environment` is set to `Production`.

Azure Function Project is `netcoreapp3.1`, in a solution with a class library which is `netstandard2.0`, the Azure Function project is set as the Startup Project.


If I use `func start --csharp` from the command line, I don't get any warnings and the `Hosting Environment` is set to `Development`.

Any ideas on where Visual Studio 2019 is getting things wrong?

Reproduce F5 debugging in Visual Studio 2019 with the netcoreapp3.1 Azure Function project and its netstandard2.0 class library, then compare it with `func start --csharp`. Check the CLI warnings and Hosting Environment value in each path; done when Visual Studio starts locally without language warnings and uses Development as the environment.

Written by the indexing model from the issue text.