Technically it's owned by .NET Foundation now, but admittedly it's composed of MSFT people by a large part. Also, language design happens on GitHub, and the community is encouraged to get involved.
As long as Microsoft finances the .NET/C# team, neither runtime/libraries nor the language will include anything which does not fit in their strategies/vision. The .NET Foundation will not change anything here. And that is good. The .NET Foundation ensures that the product is legally usable on Linux/Macs/other non Windows platforms and additionally helps the ecosystem.
