[FIX] web_editor: remove 'lang' from the context to save master website xml

addons/web_editor/static/src/js/rte.js

@@ -443,7 +443,7 @@ var RTE = Widget.extend({
                 $el.data('oe-id'),
                 markup,
                 $el.data('oe-xpath') || null,
-                context || base.get_context()
+                _.omit(context || base.get_context(), 'lang')
             ],
         });
     },