How can I send current culture to my Grpc Server in c#?

I managed to do it by adding the culture to the headers and with an Interceptor:

public class ThreadCultureInterceptor : Interceptor
{
    public override async Task<TResponse> UnaryServerHandler<TRequest, TResponse>(
        TRequest request,
        ServerCallContext context,
        UnaryServerMethod<TRequest, TResponse> continuation)
    {
        var headerLanguage = context.RequestHeaders.FirstOrDefault(t => t.Key == "language");
        if (headerLanguage != null)
        {
            Thread.CurrentThread.CurrentCulture = new CultureInfo(headerLanguage.Value);
            Thread.CurrentThread.CurrentUICulture = new CultureInfo(headerLanguage.Value);
        }

        return await continuation(request, context);
    }
}

In your Startup.cs:

services.AddGrpc(options =>
{
    options.Interceptors.Add<ThreadCultureInterceptor>();
});

On your client application:

var credentials = CallCredentials.FromInterceptor((context, metadata) =>
{
    if (!string.IsNullOrEmpty(loginResponse.Token))
    {
        metadata.Add("Authorization", $"Bearer {loginResponse.Token}");
        metadata.Add("Language", "en-US");
    }
    return Task.CompletedTask;
});

channel = GrpcChannel.ForAddress("https://localhost:5001", new GrpcChannelOptions
{
    Credentials = ChannelCredentials.Create(new SslCredentials(), credentials)
});
client = channel.CreateGrpcService<IService>();

Read about CultureInfo. This class holds a string property called Name. Commonly you just need to access the current context by doing CultureInfo.CurrentCulture.

You can also define your own culture in the server and client by setting a value on CultureInfo.CurrentCulture.

Ex:

CultureInfo.CurrentCulture = new CultureInfo("en-US");