In short, there is no Arabic Support in Silverlight 2, however there are some workarounds.  There is a specific solution from Santeon check the website, http://www.santeon.com/silverlight . You might also check out CodePlex , there are a couple of solutions, http://www.codeplex.com/SilverlightRTL and http://www.codeplex.com/SilverRTL. I downloaded and tried the first solution. It’s interesting but not bug free. There are two main tasks to add RTL support in text:

1)      Need to divide your string into rtl and ltr runs and then re-order each. In addition to right-align text.

2)      In the case of Arabic, you also need to do the shaping of characters, since the character shapes are different depending on where the character is in the word. There could be upto 4 shapes in a character, beginning form, middle form, ending form and isolated form

These are the two main tasks, of course there is additional logic of getting the text and putting it back.

This is a good attempt to add RTL support; however, there are unexpected behavior, check the issues at CodePlex.