The following Code produces different output comparing Blazor WebAssembly 3.2.0 and 5.0.0:

Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
var native = Thread.CurrentThread.CurrentCulture.NativeName;
Console.WriteLine(native);

Blazor WebAssembly 5.0.0 --> "en (US)"
Blazor WebAssembly 3.2.0 --> "English (United States)"

PS: On normal ASP-Web application running with .NET 5.0 the output is "English (United States)"