Conversion error.

[Ruby The Roobster via Digitalmars-d-learn]

I don't know any explanation for the following error:
std.conv.ConvException@D:\Programs\D\dmd2\windows\bin\..\..\src\phobos\std\conv.d(2437):
 Unexpected '\n' when converting from type LockingTextReader to type int

Here is my code for reference:

module main;

import std.stdio;
import std.concurrency;
import core.thread;
import core.stdc.stdlib;
import std.string;
int main(string[] args)
{
    Tid worker;
    int x;
    do
    {
    writeln("Enter in 1 for arabic, 2 for turkish, 0 to quit.");
    readf("%d",x);
    worker = spawn(&Translate_Hello);
    worker.send(x);
    }
    while(x != 0);
        return 0;
}

void Translate_Hello()
{
    int num;
    num = receiveOnly!int();
 switch(num)
  {
    case 1:
        stdout.writeln("مرحبا");
        break;
    case 2:
        stdout.writeln("Merhaba");
        break;
    default:
        stdout.writeln("Invalid Language");
  }
}