Delete/rebuild database when deleting a language

When we delete a language xx-XX.xml for s specific client in the languages manager and have created some translations for that language, these remain in the database, cluttering it as it is populated with all ini paths for that language and client.
This PR will purge the database when deleting a language, forcing the database to be repopulated in the managers.

To test, create an xx-XX.xml for site. Then create/save some translations for that language (no need to translate). Look the rows in the _localise table.
delete the language. Reload and look at the rows in the db.