Cloning content between locales
You could build a plugin that loops thru all the entries and creates a new entry programmatically, the only difference in the new entry would be the locale. Look at this: https://craftcms.com/classreference/services/EntriesService#saveEntry-detail, you would include $entry->locale = 'fr_us'; or whatever the shortname/handle of that locale is.

Or export the entries and import them, and setting the locale to french using something like: https://github.com/engram-design/FeedMe