VisualEditor: RTL entries don't receive dir="rtl" in Page settings / Languages

We call isRedirect to get the real language code instead of the site code.
Post-factum, lang attribute is added as well for each entry.

Bug: 53503
Change-Id: Ia6bf63a7cbe3c7b99ed05d0bd0fdd33190550c98
Merge "VisualEditor: RTL entries don't receive dir="rtl" in Page settings / Languages"