Language Sinhala unicode not working

Hi, this is my first post of wp forum. I am still new to wp. My site is https://www.lankamagazine.com and I use wp 2.8. My problem is our local language Sinhala unicode is not working in my wordpress site. When I type something it shows clearly but when I post it it just shows “?????”
for ex if I type – “?????”(I am sure you can see it) it shows in my site “?????” Please help me. I believe that uni-code problems are common to any language that Wp supports. I just installed a fresh copy of wordpress and tried. It supported unicode successfully. According to my opinion it is a problem with database but I am not sure about it and I can’t find it. Please help me to solve this problem.
thanks.