mIRC doesn't read Arabic fonts..
What can I do?

Chadi.

You'll need to install the appropriate font in Windows. I'm not sure what font you would need for Arabic.

I installed all the Arabic fonts.

Ok... now you have to use them. You can either change your channel font to an arabic font and it should work fine, though non-Arabic text may be messed up. Or, you can turn on the UTF-8 and Font Linking and, if you are lucky, the Arabic fonts will be included in the Font Linking so it will find those automatically. I'm not sure what all is included with font linking as I don't use it.