I think that reference to "other than prosilver or subsilver2" may be incorrect. Should that really say "If you are using a style that is not based on prosilver you will need to copy...." instead?NB: If you are using a style other than prosilver or subsilver2 you will need to copy the /styles/prosilver/theme/XX folder in to into the theme folder of your custom style.
Also, those instructions don't say anything about the language packs containing a folder named /ext, and also needing to upload that to the board. That part of the instructions should probably be updated.