In CSS you can not have all the subjects or your choice. There are some rules to follow and restrictions in subject selection.

AS you are interesting in Arabic Language i suggested you to opt Punjabi. To learn Punjabi is more easy as compare to Arabic. If you can read and write Urdu then you can easy read and write Punjabi.
Punjabi is a 100 marks subject and it is a scoring subject as languages are supposed to be again i mention that there is no exact criteria in all CSS. as i mentioned earlier i got 38 in Punjabi in 2007 but 73 in 2008. The course outline of Punjabi seems lenghty but it's an easy subject to handle. I have Computer Science Background and i did not opt Computer Science and opted punjabi.

For subject Selection I have devised the following simple but effective method. After working on it you will feel confortable in deciding your optionals. Dont waste mush of your time in deciding your optional and once you choose you are not gona change them.

First read the syllabus slowly and very clrealy and understand topics mentioned and sub-topic. Then read past papers of at least 10 years (It is better to sort out all question by writing them on paper with respect to a specific topic).

Now repeat this practice three times, after that you must have enough clearity, courage and determination to opt a subject.

I hope you will work on this method. The other potential benefits to choose a sbject is that how much easily you can prepare it, means have you its notes, guidance, books and paper attempting and preparing techniques in your hand or you are just preparing you own why by hit and trial method.

Although there is a unique study method to prepare each CSS subject but there is a slight difference in preparing each subject which also helps you to get extra marks in it. I will discuss the study method first and paper attempting techniques later.

hope this reply will help u.
comments are welcome