In SQL Server Management Studio (SSMS) 18.2, Arabic is displayed as the default language for all SQL Server and Windows logins across all versions of the SQL Server database engine from 2008, 2012, 2014, 2017 including the 2019 preview version.
A review of the Server Properties > Advanced page shows English as the Default Language for the SQL Server instance.
A query (shown below) on the sys.server_principals correctly returns us_english as the default language name, therefore, this is only a UI display issue.
select name, default_language_name from sys.server_principals
Microsoft has been made aware of this default language display issue with SSMS 18.2 and is working on a fix for a future SSMS release.