The file format (SHP) it's documented in the AutoCAD customization guide, SHX files are SHP compiled for AutoCAD (using the compile command), but creating a brand new font file may be a very tedious task, pehaps this link may help You: Arabic Fonts.
Our software handles this type of thing but slightly differently: Our English software has an .SHX font. But when we started to develop an Arabic version we found we couldn't do it easily, as the Arabic font characters change depending on where they are in the word. It was a pretty complex process I can tell you. If you used an Arabic SHX font you would have to map nearly the full 256 characters of the alphabet to an individual key on the keyboard. We felt this was unpractical and completely unusable for a "user". The way we did it was to create a virtual Arabic keyboard that you type your destinations/words into. It "glues" the letters together and you then insert the result as a series of blocks