Add Language Packs to Image VMs
Windows 10 Multi-Session images only come with English pre-installed. To support other languages for your AVD users, you need to install the language packs directly on the Image VM that your host pools are based on.
Warning: Installing language packs incorrectly via other means, such as pre-existing GPOs, can cause the Sysprep to fail. Language packs must be installed in a manner that Windows 10 multi-session supports.
Nerdio recommends following a procedure similar to Microsoft's process as defined here. With the exception that instead of initiating Sysprep on the image VM itself, to initiate it from the Nerdio Manager Images page.
Tip: For the file share requirement, you can add a file share to the existing storage account you may be using already for FSLogix. See this Microsoft document for details. This can be useful to keep resources consolidated, and allows you to simply use permissions you already have granted for FSLogix on the storage account.