code: Set<Locale> getImplLocales(Class<?> c10nInterface) {
          Set<Locale> res = new HashSet<Locale>();
          C10NImplementationBinder<?> binder = binders.get(c10nInterface);
          if (binder != null) {
              res.addAll(binder.bindings.keySet());
          }
          return res;
      }
docs: Find all locales that have explicit implementation class
  bindings for this c10n interface.
  
  @param c10nInterface interface to find bindings for (not-null)
  @return Set of locales (not-null)