I'm baffled. I've added boot.wim from 8.1 RTM and 2012 R2 RTM to a new WDS installation. The default language is en-us according to the file properties in WDS, but it errors out on the client with: failed to set the selected language as the UI language. I cannot set it to en-us. It works for any other English variant - just not the US. I can get it work, for example, as English (Canada) with a US input. But not English (united states).
Jason Yates