Generate multilingual books

lib/output/generateBook.js

@@ -1,3 +1,4 @@
+var path = require('path');
 var Immutable = require('immutable');
 
 var Output = require('../models/output');
@@ -94,6 +95,21 @@ function generateBook(generator, book, options) {
     .then(generateAssets.bind(null, generator))
     .then(generatePages.bind(null, generator))
 
+    .tap(function(output) {
+        var book = output.getBook();
+        var books = book.getBooks();
+        var outputRoot = output.getRoot();
+
+        if (!book.isMultilingual()) {
+            return;
+        }
+
+        return Promise.forEach(books, function(langBook, language) {
+            var langOptions = options.set('root', path.join(outputRoot, language));
+            return generateBook(generator, langBook, langOptions);
+        });
+    })
+
     .then(callHook.bind(null,
         'finish:before',
             function(output) {