“All features of the Mac version are planned for inclusion in the Windows version. We can’t provide any specific dates, but anything you see in the Mac version will be coming to the Windows version if it’s not there already.” (emphasis added).
I think KB missed the word “eventually” on that one
In fact, I’m not sure if this applies in this case. There’re some limitations on the spelling engine used on Windows & Linux regarding this matter, and IMHO doing it exactly like Mac OS does for their apps on this is a major endeavour.
Some users have requested at least a per-project language setting, but I don’t know if that’s already on the queue or not (I’m just a Scrivener fan, not a developer).
The language features on Mac are entirely provided by OS X; Scrivener doesn’t do anything with any of that. Windows does not have a similar feature, sadly, and we’re not in a position to develop an equivalent suite of language tools. We’re looking into different dictionary options for the next major version of Scrivener on Windows, and we’re aware that there’ve been requests for a per-project dictionary, but whether that’s something Scrivener will ever be able to handle, I can’t say. If we are able to do it, it’s on the list.