Entire question is in the title: Are there any working, and tested, JSon serializer implementations for .NET 4?
I tried Json.NET on codeplex, but it is neither updated for .NET 4.0, nor does it handle culture differences (like comma/dot in floating point values).
Are there any that works?
Aren’t the ones built-in the framework working in your scenario (JavaScriptSerializer and DataContractJsonSerializer)? Those are guaranteed to be working and tested.