Show a list of recently used tags only from the current locale
Brandon at P&amp;T was able to fill in the piece I was missing. He said:

To only get tags that were related from a specific locale, you just need to specify that in your relatedTo param:

    {% set tags = craft.tags.relatedTo({
      sourceElement: entries,
      sourceLocale: craft.locale
    }) %}


With the addition of order('dateCreated desc').limit(10) to put some additional constraints on what I was getting back, this solved it for me.