Bulk update lat/long taxonomy terms
Have you looked at Geofield and Geocoder modules?

I believe you can configure the geofield as a field on your taxonomy to hold the Lat/Lng. Then, you can configure your geofield widget as Geocode from another field.

For batch back-filling, Geocoder provides the drush command:  

geocoder-backfill     Geocodes all nodes that have a geocoder widget but no geodata.