You are right, according to this document, en-AE locale is only available on Windows 10/Server v2004 and later versions.
So you might have 2 options here depending on where your application is deployed.
- If your application is deployed to VMs on which the OS is the older version of Windows, you can use this tool, Locale Builder 2.0, to build a custom locale for en-AE and install it on the VMs. You might not need to change your code in this way.
- If your application is deployed to App Service or other PaaS services on which you cannot deploy custom locales, you would want to consider moving your code to .NET 5. The globalization of .NET 5 uses ICU by default. You can use an app-local ICU which supports en-AE.
Hope it helps. Thanks.