Fix plugins for multi languages
Fix plugins for multi languages

The plugin was not migrating the metadata for non default languages, this patch
fixes that.

lotabout/plugins,pluser/nikola_plugins,s2hc-johan/plugins,getnikola/plugins,getnikola/plugins,getnikola/plugins,lotabout/plugins,pluser/nikola_plugins,s2hc-johan/plugins,s2hc-johan/plugins,pluser/nikola_plugins,lotabout/plugins