So if I'm not mistaken (my wife's family is of Lebanese descent, so I did short course on Arabic years ago; also I had to learn a little when I was working on LibreOffice) but the difficulties with Arabic are:
- Each character can have a final, medial or initial form; it all depends on where the character is located in the word
- it's a cursive script, so letters join together...
- it uses ligatures in (what appears to me at least) complex ways
- kashida elongates letters, but there are typographic and aesthetic rules for when and how it should be used.
- there are complexities galore around diacritics [1] and text justification [2]
- Each character can have a final, medial or initial form; it all depends on where the character is located in the word
- it's a cursive script, so letters join together...
- it uses ligatures in (what appears to me at least) complex ways
- kashida elongates letters, but there are typographic and aesthetic rules for when and how it should be used.
- there are complexities galore around diacritics [1] and text justification [2]
1. http://arxiv.org/pdf/1107.4734.pdf
2. http://www.tug.org/tugboat/tb27-2/tb87benatia.pdf