Fixed #23005 -- Allowed specifying special fallback languages

This fixes the Chinese language issues described in #23005 but
also provides for other fallback exceptions by updating the
LANG_INFO structure.
Thanks caxekis at gmail.com for the report and Tim Graham for the
review.
Fixed #22970 -- Use last migration's name in dependency to existing migrated app

Changed the autodetector to lookup the name of the existing app's last
migration in the graph and use that as dependency.