problem persian language asp ajax?

There is no such problem. ASP.NET supports Unicode simply because all .NET strings are Unicode. Ajax is based on Javascript which also support Unicode. The only rule is: you should generate all HTML content in UTF-8 encoding (it could be with BOM or without it — does not matter), and the HTML header should have matching http-equiv declaration:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

Unicode is also supported by all modern Web browsers. I you do not follow the encoding rule I described above, many Unicode characters will be converted to '?'. (The question is about those '?' characters, as I could understand using Google Translate.)

Now, the question is Persian language presently uses Perso-Arabic script, see http://en.wikipedia.org/wiki/Persian_alphabet[^]. This writing system is totally placed in Base Multilingual Plane (BMP, code points < 0x10000 which requires 16 only bit in UTF-16, not 32 bits required by some more exotic writing systems). Also, it is popular enough to be supported by nearly all modern platforms.

I cannot speak Persian or Arabic at all, but even I had written in Persian (with the help of my colleague who knows the language well) to test my software. I'm sure you will be able to do so, too. :-)

See:
http://unicode.org/[^],
http://unicode.org/faq/utf_bom.html[^].

—SA