Q:

Flash player does not work probably with Arabic language

The Flash plug-in version 11.2 which is the latest version does not support the Arabic language. 
It shows the characters separated and oriented from left to right; whereas it has to display them as joined characters and oriented right to left. 
Adobe says that they will only provide a security update and nothing else, so that clear bug will be kept for Firefox, Opera and other browsers that depend on the standalone plug-in. 
Google Chrome display the language correctly because of it's own built in plug-in.

A:

Since Adobe will not update flash for Linux.  

Adobe will no longer provide new releases of Flash Player for Linux
  after version 11.2, the company has today announced.
Google will, instead, take over the implementation of Flash Player via
  a new plugin API called ‘Pepper‘.1

Consider using HTML 5 instead of flash for You Tube.  It doesn't have that problem.  As you see in the below image, it doesn't have the problem.
1Source:OMG

