Arabic language in CakePHP

I have seems to be in a deep trouble when I try to display Arabic language fonts in my cakephp website. When I am displaying them in the drop-downs,it shows black colored diamonds and when I try to display them through JSON,it display the following error:

Invalid multibyte sequence in argument

Now I have using ‘utf-8’ encoding in the html pages. I have also tried using other encoding such as ‘windows-1256’ but it didn’t worked either.

Please anyone can tell me what might be reason for this problem and any solution to it?
Thanks in advance.