Fix support for site where lang != code

APISite.lang may change based on the siteinfo.
For local files, the family 'lang' code should be used.
e.g. This code may be 'wikidata' or 'commons'.

Change-Id: If71b3ab3e7ad14f873862954457b0cd7f0efb646
Merge "Fix support for site where lang != code"