You have to follow the documentation to set the local variable that the browser should use :
Set the SMSERVERLOCALE Response Header Variable in the UI
A policy administrator can use the Administrative UI to set the preferred locales in which the Policy Server serves a request.
To set preferred locales as a response, use the SMSERVERLOCALE response attribute.
Follow these steps:
Log on to the Administrative UI.
Click Policies, Domain.
Edit a response that you want to modify.
Click the Define Response tab.
Edit the Response Attribute that you want to modify.
Select the Attribute Type as WebAgent-HTTP-Header Variable.
Type SMSERVERLOCALE in Variable Name.
Type the preferred locales in Variable Value.
Save the changes.
Extracted from: https://docops.ca.com/ca-single-sign-on/12-52-sp1/en/configuring/web-agent-configuration/fcc-internationalization
The value to be changed should be as follows:
For Arabic, you may use the following value :