Necroposting! 
So, I just translated all of the pages and templates on WriteFreely 0.15.1 into Spanish, and as far as I can tell, all of the user-facing content is completely translated, except for some page titles.
I think the page titles on the pages not able to be changed from the templates can be set using JavaScript document.title, but I have not really tried it.
I do have the files on my PC, but I’m not really sure how to share them