Thread.CurrentThread.CurrentCulture not working in a thread inside a threadpool

I have a method which will be called inside a thread and those threads are managed by threadpool. The method is calling a DLL's method which unfortunately requires a specific locale for being performed correctly.

Before puting this method to be ran by threadpool, I've tested it while running in application's main thread and also while I manually manage the threads and it works fine, but when I put it into work inside a threadpool, locale is not applied and consequently the method does not behave correctly.

Here is the part of the method which should be affected by locale change (but not behave well):

CultureInfo before = Thread.CurrentThread.CurrentCulture;

Thread.CurrentThread.CurrentCulture = new CultureInfo("fa-IR");
int result = tsms.SendSMS(smsTask.MobileNumber.MobileNumberInString, smsTask.Message);
Thread.CurrentThread.CurrentUICulture = before;

and here is the threadpool creating structure:

foreach (SMSTask smsTask in tasksList)
{
    if (this.threadsCount < this.threadPoolSize)
    {
        this.threadsCount++;                        
        ThreadPool.QueueUserWorkItem(new WaitCallback(SendMessage), (object)smsTask);
    }
}

I also tried setting locale to thread object like below but it didn't solve the problem: (line 2 and 3):

threadObject = new Thread(new ThreadStart(TaskProcessingThreadFunction));
threadObject.CurrentCulture = new CultureInfo("fa-IR");
threadObject.CurrentUICulture = new CultureInfo("fa-IR");
threadObject.Start();

Please guide me on how should I get the correct result while this method is being ran inside threadpool.

Updated Version:

this.isTerminated = false;
            Thread.Sleep(1000);
            while (!this.isTerminated)
            {
                Thread.Sleep(1000);
                IList<SMSTask> tasksList = dataProvider.GetTasks(this.minimumRetryTimeInSeconds);

                if (tasksList == null || tasksList.Count < 1)
                    continue;
                singleTaskConsoleObject(" " + tasksList.Count + " task(s) fetched for sending.");

                var cultureToUse = new System.Globalization.CultureInfo("fa-IR");
                var currentThread = System.Threading.Thread.CurrentThread;
                currentThread.CurrentCulture = cultureToUse;
                currentThread.CurrentUICulture = cultureToUse;

                var currentIdentity = System.Security.Principal.WindowsIdentity.GetCurrent();
                foreach (SMSTask smsTask in tasksList)
                {
                    if (this.threadsCount < this.threadPoolSize)
                    {
                        this.threadsCount++;
                        smsTask.Iden = currentIdentity;
                        ThreadPool.QueueUserWorkItem(new WaitCallback(SendMessage), (object)smsTask);
                    }
                }
                while (this.threadsCount > 0)
                    Thread.Sleep(50);
            }

Other Methods:

private void SendMessage(object smsTask)
        {
            System.Security.Principal.WindowsImpersonationContext impersonationContext = null;
            try
            {
                SMSTask smsTaskEntity = (SMSTask)smsTask;
                impersonationContext = ((System.Security.Principal.WindowsIdentity)(smsTaskEntity.Iden)).Impersonate();

                SmsSender smsSender = new SmsSender();
                SMSSendingResponse response = smsSender.SendSMS(smsTaskEntity);
                bool loggingResult = dataProvider.UpdateResponse(response);
                singleTaskGridObject(response, loggingResult);

                this.threadsCount--;
            }
            finally
            {
                if (impersonationContext != null)
                {
                    impersonationContext.Undo();
                }
            }
        }

And this separate class:

public SMSSendingResponse SendSMS(SMSTask smsTask)
{

        TSMSLIB_TLB.TSMS_Tooba tsms = new TSMS_Tooba();

        SendingResult sendingResult = SendingResult.Initial_Condition;
        try
        {

            System.Globalization.CultureInfo before = System.Threading.Thread.CurrentThread.CurrentCulture;

            System.Threading.Thread.CurrentThread.CurrentCulture =
                new System.Globalization.CultureInfo("fa-IR");

            string msg = string.Format(System.Threading.Thread.CurrentThread.CurrentCulture, smsTask.Message);

            int result = tsms.SendSMS(smsTask.MobileNumber.MobileNumberInString, msg);
            System.Threading.Thread.CurrentThread.CurrentUICulture = before;
            if (result > 0)
            {                    
                return new SMSSendingResponse(smsTask, SMSDeclarations.SendingStatus.SentSuccessfully, result.ToString());
            }
            else
            {
                foreach (SendingResult sResult in Enum.GetValues(typeof(SendingResult)))
                {
                    if (result == (int)sResult)
                    {
                        sendingResult = sResult;
                    }
                }
                return new SMSSendingResponse(smsTask, SMSDeclarations.SendingStatus.SendingFailed,
                    result.ToString(), sendingResult.ToString());
            }
        }
        catch (Exception ex)
        {
            return new SMSSendingResponse(smsTask, SMSDeclarations.SendingStatus.SendingFailed,
                    "0".ToString(), "Exception occured");
        }

    }