Deploying Win10 with Windows Deployment Services

The language value is actually coded into each .wim file. it defaults with a new wim to en-US.

You can use the dism tool in waik to set the language value on the wim image. Specifically the /Set-UILang switch.

Check out the following documentation page for more information:

http://technet.microsoft.com/en-us/library/dd744360(WS.10).aspx

There is no WindowsPE pass in your unattend. The very first example in this article is an example of a WindowsPE pass for WDS that should help you get past those initial prompts for language and setting up the hard drive. If you continue using MDT, you don't have to set much of this in the unattend file, since you can do all of this in the Task Sequence, and using the MDT LiteTouch.wim files as your boot images in WDS will let you choose the Task Sequence upon PXE boot. More information on the WindowsPE pass can be found in this article.