How do I change the position of "sidebar first" for the Arabic version of website?
Install the Context module. 


  Context allows you to manage contextual conditions and reactions for
  different portions of your site. You can think of each context as
  representing a "section" of your site. For each context, you can
  choose the conditions that trigger this context to be active and
  choose different aspects of Drupal that should react to this active
  context.


Make sure that Multilingual select which is part of the Internationalization module is also installed (this will provide the proper condition).

You can now create a new context that has a condition of 'Language' and a reaction of 'Blocks'.

You will create a condition-reaction pair for two cases. First for all the LTR languages, second for all the RTL languages.

Allthough this does not directly answer your question as to regions, you can play around with the reactions, such as template suggestions etc to achieve your objective.